Manual 6 – Embedded corrosion of fasteners in …€¦ · Manual 6 – Embedded corrosion of fasteners in exposed timber structures PROJECT NUMBER: PN07.1052 August 2007 MARKET

Manual 6 – Embedded corrosion of fasteners in exposed t imber structures

PROJECT NUMBER: PN07.1052

August 2007

MARKET ACCESS

This report can also be viewed on the FWPA website

www.fwpa.com.auFWPA Level 4, 10-16 Queen Street,

Melbourne VIC 3000, AustraliaT +61 (0)3 9927 3200 F +61 (0)3 9927 3288

E [email protected] W www.fwpa.com.au

USP2007/043

MANUAL NO. 6

Embedded Corrosion of Fasteners in

Timber Structures

Minh N. Nguyen, Robert H. Leicester, and Chi-hsiang Wang

April 2008

This report has been prepared for Forest & Wood Products Australia (FWPA).

Please address all enquiries to:

Urban Systems Program

CSIRO Sustainable Ecosystems

P.O. Box 56, Highett, Victoria 3190

Manual No. 6: Embedded Corrosion of Metal Fasteners in Timber Structures 2

Acknowledgments

This Manual is one of a series of Manuals that have been produced as part of a project titled

„Design for Durability‟. The authors are deeply indebted to the Forest and Wood Products

Australia for their funding and collaboration in this project over the past 10 years. The authors

would especially like to thank Colin MacKenzie (Timber Queensland) for the major role that

he has played in managing and guiding this project to completion. Thanks are also due to Ivan

Cole (CSIRO), Wayne Ganther (CSIRO), and George King (ex-CSIRO) for contributing

extensive data and expertise to the development of the models described in this Manual.

Finally our thanks go to Greg Foliente, Craig Seath, Sandra Roberts and numerous other

CSIRO personnel for their assistance and contribution to this project

© 2008 CSIRO

To the extent permitted by law, all rights are reserved and no part of this publication covered by

copyright may be reproduced or copied in any form without acknowledgment of this reference source.


Contents

EXECUTIVE SUMMARY

1. MODEL EQUATIONS

1.1 Introduction

1.2 Scope and Procedure

1.3 Timber Acidity Classification and Hazard zones

1.4 Moisture Content of Timber

1.5 Corrosion Depth of embedded fasteners in untreated wood

1.6 Corrosion Depth of Embedded Fasteners in CCA treated wood

1.7 Design Depth of Embedded Corrosion

2. BASIS OF MODEL DEVELOPMENTS

2.1 Introduction

2.2 Timber Moisture Content model and Hazard Zones

2.2.1 Surface Equilibrium Moisture Content of Timber

2.2.2 Hazard Zones and Climate Zones

2.2.2.1 Hazard zones

2.2.2.2 Climate Zones

2.2.3 Timber Moisture Content

2.3 Timber Acidity Classification

2.3.1 Timber Acidity

2.3.2 Timber Classification

2.4 Model Equations of Embedded Corrosion

2.4.1 The Base Model of Embedded corrosion in untreated wood

2.4.2 The Base Model of Embedded Corrosion in CCA treated wood

2.4.3 Mean Corrosion Depth

2.5 Design Corrosion Depths

2.5.1 Coefficient of variation

2.5.2 Design Corrosion Depths

2.6 Corrosion of Bolts

3. DATA FITTINGS

3.1 Fitting and calibration using data of 2-year embedded nails exposed to in-service

conditions

3.2 Fitting with data from BRANZ Study Report of Embedded Corrosion Tests

3.3 Fitting with 120-day embedded corrosion tests

4. HAZARD SCORE SYSTEM

4.1 Definition of Hazard Scores

4.2 Definition of Hazard Class

4.3 Derived c0 values

4.4 Corrosion depths

4.5 Service Life


5. EQUATIONS FOR THE DRAFT ENGINEERING CODE

6. SCORE SYSTEM FOR THE DESIGN GUIDE

REFERENCES

APPENDIX A – Derivation of Score System to estimate Timber Moisture Contents

APPENDIX B – Moisture Contents & First-year Corrosion Depths for Theoretical

Corrosion Scenarios

APPENDIX C – MODEL EQUATIONS 2000

C.1 Introduction

C.2 Acidity of Timber

C.3 Corrosion Model

C.3.1 The Base Corrosion Model

C.3.2 Parameters for Untreated Wood

C.3.3 Parameters for CCA-treated Wood

C.3.4 Moisture Content of Timber

C.3.5 Computation of Corrosion Depth

C.4 Data from nails embedded in timber for 120 days under constant moisture content

APPENDIX D – MODEL EQUATIONS 2002

D.1 Hazard Zones

D.2 Climate Zones

D.3 Material Grouping

D.4 Simplified Theory Equations

D.4.1 The Base Model of Embedded Corrosion in Untreated Wood

D.4.2 The Base Model of Embedded Corrosion in CCA-treated Wood

D.4.3 Moisture Content of Timber

D.4.4 Corrosion Depth

APPENDIX E – HAZARD SCORE SYSTEM 2002

E.1 Definition of Hazard Scores

E.2 Definition of Hazard Class

E.3 Derived c0 values for computing the tables in the 2002 Compendium

E.4 Service Life


Executive Summary

Service life is one of the most important considerations in the use of timber in construction.

About 10 years ago, the Forestry and Wood Products Research and Development Corporation

(FWPRDC), now Forest & Wood Products Australia (FWPA), initiated a major national

project on the design for service life of timber structures. The intention was to develop

procedures for assessing the service life of all types of timber construction located anywhere

in Australia. A major part of this project was to develop prediction models for the attack of

timber by decay fungi, termites, corrosion (for fasteners) and marine borers.

This Manual describes the development of the model to predict the corrosion of fasteners‟

part embedded in wood. The model was primarily developed based on expert opinions and

data obtained from an extensive test program of about 70 nails embedded for 120 days in 15

different timber species and/or preservative treatments. The model was then fully developed

so that it can be applied to all locations in Australia, and to numerous timber species used in

practice. Checks and calibration of the model were then carried out with about 150 corrosion

data of nails from a test of 2-year exposure of nail joints at various locations in 8 houses in

VIC, NSW, and QLD; and with the results of a Lab study by BRANZ on corrosion of metallic

fastener materials in Radiata pine untreated and treated with CCA.

From the predicted corrosion depth, the residual cross-sections of fasteners can be estimated.

The strength predictions for the residual cross-sections can then be made. The strength

predictions are in quantified form, and hence the model can be used for risk managements,

cost-optimised design, engineering design, application to timber engineering standard, and

manuals for good practice. For the major outputs of the project, the model is being used to

develop a major part of an education software, a durability design guide, and a draft

engineering code for timber durability design.


1. Model Equations

1.1 Introduction

This Section presents the final model and the calculation procedure for the design corrosion

depths on embedded parts of metal fasteners, which can be used to estimate the corrosion

depths for metal fasteners used in any timber construction located anywhere in Australia.

Basis of the development of model equations will be given in Section 2. Then Section 3 will

show how available data fit with the model.

1.2 Scope and Procedure

This Section provides the calculation procedures for the design corrosion depths on metal

fasteners‟ parts that are tightly embedded in wood, such as the shank of nails, screws, and

nailplate‟s teeth, as depicted in Figure 1.2.1.

To evaluate the design corrosion depths, the timber acidity class and hazard zone of the

structure location are obtained from Section 1.2.1. Timber moisture content is estimated from

Section 1.2.2. The mean corrosion depth is then estimated using the procedure in Section

1.2.3 for fasteners embedded in untreated wood, and Section 1.2.4 for fasteners embedded in

CCA-treated wood. The design corrosion depths are then determined in Section 1.2.5.

Loss of section of embedded steel

c

Figure 1.2.1 Embedded corrosion depth

1.3 Timber Acidity Classification and Hazard zones

Durability classification of timber is listed in Section 2.3.

The hazard zone map is shown in Figure 1.3.1. Three hazard zones and their representative

mean annual surface equilibrium moisture content SEMCmean and the boundary SEMCmean are

in Table 1.3.1.


Table 1.3.1 Effective SEMCmean values for the 3 hazard zones

Zone SEMCmean

A

B

C

9

12

15

Figure 1.3.1 Embedded corrosion hazard zone map. Zone C is most hazardous.


1.4 Moisture Content of Timber

The mean annual surface equilibrium moisture content, SEMCmean, is given in Table 1.3.1,

depending on hazard zones. The mean seasonal moisture content of a piece of timber, TMmean

for one year is estimated as,

TMmean = exp(1.9 + 0.05 SEMCmean) (1.4.1)

The mean and maximum seasonal moisture contents of timber in building, BTMmax and

BTMmean, are:

mean mean climate rainBTM TM (1.4.2)

max mean mean0.1 BTM BTM D TM (1.4.3)

where the damping factor (D), the adjustment factors for the climate (climate) are given in

Tables 1.4.1. The adjustment factor for rain (rain) is given in Table 1.4.2.

Table 1.4.1 Damping factor and adjustment factor for climate

Climate zone D Δclimate

Marine*

Other

6.0

2.0

2.5

0.5

* Marine: if the distance to coast < 1 km

Table 1.4.2 Adjustment factor rain

Outdoor (Facades) rain

Hazard zone A Hazard zone B Hazard zone C

Sheltered / partly sheltered from rain

Vertical surface exposed to rain

Horizontal surface exposed to rain

0

1

3

1

4

9

2

8

17

Note: For corrosion of bolt’s shank (see Section 2.5), this factor is increased by 1.5 times.


1.5 Corrosion Depth of embedded fasteners in untreated wood

For the case of untreated wood, corrosion depth for the first year (m), co is computed as

follows,

o 120 max 120 mean

1( ) 0.3 ( )

2c f BTM f BTM (1.5.1)

where f120(M) is the corrosion depth of connectors embedded in untreated wood for 120 days,

given as a function of timber moisture content M (%),

0

120 120 0 0 0

120 0

0 if ;

( ) 0.2 ( ) if ( +5%);

if ( +5%)

M M

f M C M M M M M

C M M

(1.5.2)

The function is illustrated in Figure 1.5.1. Values of C120 and M0 are listed in Table 1.5.1

depending on the timber acidity class and timber type.

Moisture content

of wood

M (%) M0

C120

Corrosion depth (m)

f120(M)

In untreated wood

M0 +5%

Figure 1.5.1. Base model of embedded corrosion in untreated wood.

Table 1.5.1 Parameters of the corrosion model of embedded fasteners in untreated wood

Material Wood type

C120

M0 (%) Acidity

class 1

Acidity

class 2

Acidity

class 3

Zinc Hardwood 2.0 7.0 12.0 10

Softwood 4.0 5.0 6.0 15

Steel Hardwood 2.0 8.0 14.0 15

Softwood 2.0 6.0 10.0 15

The corrosion depth of embeeded fasteners in untreated wood, c, over the period t years is

computed by

c = co tn (1.5.3)

where n= 0.5 for zinc and n = 0.6 for steel.


1.6 Corrosion Depth of Embedded Fasteners in CCA treated wood

For the case of CCA-treated wood, corrosion depth for the first year (mm), co is computed as

follows,

For zinc o 120 mean1.3 ( )c f BTM (1.6.1)

For steel o 120 mean2.1 ( )c f BTM (1.6.2)

where f120(M) is the corrosion depth of connectors embedded in CCA-treated wood for 120

days, given by

0

120

0 0

0 if ;( )

0.7 ( ) if ;

M Mf M

M M M M

(1.6.3)

where M is moisture content, M0 = 12%. The function is illustrated in Figure 1.6.1.

Moisture content of wood

M (%) 12

C120

Corrosion depth (mm)

f120(M)

In CCA treated wood

wood

0.7

Figure 1.6.1. Base model of embedded corrosion in CCA-treated wood.

The corrosion depth of embedded fasteners in CCA-treated wood, c, over the period t years is

computed by

c = co tn (1.6.4)



1.7 Design Depth of Embedded Corrosion

The design depth of embedded corrosion, cdesign will be given by

1design cc c V (1.7.1)

where

c is the mean depth of the loss in fastener cross-section due to embedded corrosion,

computed by Eq.(1.5.3) or Eq.(1.6.4) for a chosen design life time.

Vc is the coefficient of variation of c. From available data, it is recommended that Vc =

2.0.

is specified parameter related to the target reliability level.

= 0.8 for normal consequence of failure elements.

= 0.4 for low consequence of failure elements.

From the design depth of embedded corrosion, the residual cross-section is estimated; from

which engineers compute the acceptable design load capacity by normal AS1720.1 procedure.


cb

Corrosion

Figure 1.8.1 Depth of corrosion at the neck of the bolt

It is known that bolted joints can form a very special case of embedded fastener, because they

are often placed in oversized holes pre-drilled into the timber, thus allowing moisture/water,

salt and oxygen to enter, a situation that does not occur with other fasteners. To provide some

sort of indication of the corrosion of bolts, an assumption is made that the worst corrosion

occurs near the neck of the bolt, and this is either due to the embedded corrosion mechanism

that is enhanced by water ingress into the bolt‟s hole; or due to atmospheric corrosion that is

enhanced if the connector is near a beach. The procedures are as follows,

To compute the corrosion depth due to the embedded corrosion, follow the procedure in

Sections 1.2 to 1.7, with a modification that the adjusted factor rain (Table 1.4.2) is

multiplied by factor of 1.5 to take into account the increasing of timber moisture content

due to water ingress into the bolt‟s holes.

To compute of the corrosion depth due to atmospheric corrosion that is enhanced if the

connector is near a beach, follow the procedure in Manual No.5.

The corrosion depth cb near the neck of the bolt is taken to be the higher of these two

computed corrosion values.


2. Basis of Model Development

2.1 Introduction

This Chapter presents the basis of the development of the corrosion model for embedded part

of fasteners (embedded corrosion) in wood. There are 2 main parameters contributing to the

extent of the embedded corrosion in wood: (1) Timber moisture content, and (2) Acidity of

wood or preservative used. These 2 main parameters will be addressed in the followings.

2.2 Timber Moisture Content model and Hazard Zones

2.2.1 Surface Equilibrium Moisture Content of Timber

The surface equilibrium moisture content (SEMC) for a given temperature and humidity is

calculated according to Bramhall‟s equation (Siau, 1995) as follows:

ee 2

e

log ( /100) 0.0251log

17.884 0.0002362( 273) 0.1432( 273)

0.92 log 1.0327 0.000674( 273)

H

T TSEMC

T

(2.2.1.1)

where

T = the dry bulb temperature (C)

H = relative humidity (%)

The SEMC can be calculated with time, using data from a nearby Bureau of Meteorology

station, and then be averaged to obtain SEMCmean, the mean annual value of the surface

moisture contents. This parameter will be used as the main parameter to predict the timber

moisture content with a model developed in Section 2.3.

2.2.2 Hazard Zones and Climate Zones

2.2.2.1 Hazard zones

To simplify the calculation procedure, 3 hazard zones, namely A, B and C; are created as

shown in Fig. 2.2.2.1. This original map is plotted from the computed SEMCmean from

weather data measured at hundreds of Bureau of Meteorology (BOM) stations across

Australia, with an adjustment due to the simplification of the climate zones. The adjustment

has been made to the tropical areas, which have latitudes less than 23˚ S, where the SEMCmean

data was increased 1% to compensate for using the simplified values of Δmicroclimate for climate

zone „other‟, ie. non-marine, as in Table 2.4.3.3. This will be defined as the Effective

SEMCmean. The simplified climate zonation is presented in the next section.


A B

C

Figure 2.2.2.1. „Original‟ hazard zone map based on SEMCmean.

Furthermore, expert opinions (MacKenzie) suggested that zone C should not be cut out along

the coast near Brisbane. Figure 2.2.2.2 is the modified map currently used. The modification

was made by adjusting the SEMCmean at Gympie (BOM data point C62) from 12.38% to 13%.

The boundary and the zone effective SEMCmean values are in Table 2.2.2.1.

Table 2.2.2.1 Effective SEMCmean values for the 3 hazard zones

Zone Zone effective

SEMCmean

Effective SEMCmean

used for boundary

A

B

C

9

12

15

10

13


Figure 2.2.2.2. Hazard zone map

2.2.2.2 Climate Zones

In the early model presented in Appendix C, there were 6 climate zones, which were:

Defined with a quite complicated procedure to determine the zone of a site

Assigned with different values of many factors relating to climate and microclimate.

However, we noted that the factors relating to climate and microclimate were very rough

estimates which were about right for some tested houses/sites only. And as long as we are

only interested in the model for façade/exposed structures, significant differences of the

values of these factors are only found between „Marine‟ zone and the rest. Therefore, we

simplified the climate zonation by defining only 2 climate zones:

Marine: if the distance to coast < 1 km

Other, ie. non-marine

The factors relating to climate and microclimate are also simplified, as listed in the next

section.

2.2.3 Timber Moisture Content

The early model for moisture content of timber is presented in Appendix C, which was

developed based on a test program presented in Cole et.al. (1996a, 1996b, 1999), Ganther &

Cole (2000), and Cole (private communication and internal reports). A summary of the test

program is provided in Section 3.1. In 2002, based on expert opinions from Mackenzie

(2000), we modified the model with another factor rain to take into account the orientation


and sheltering effects of the structures. The modified model in 2002 is presented in Appendix

D.

This section presents the final model to estimate the moisture content of the timber.

Borrowing some ideas of simplification made for the development of the Score System

presented in Appendix A, the 2002 timber moisture content model in Appendix D is further

simplified, as presented in the followings.

The mean and the maximum seasonal moisture contents of a piece of timber for one year as

follows,

TMmean = exp[1.9 + 0.05 SEMCmean] (2.2.3.2)

TMmax = 1.1 TMmean (2.2.3.3)

where TMmax = the maximum value out of the four TM seasonal values of moisture content in

a piece of timber for one year, TMmean = the mean annual value of timber moisture content.

The mean surface equilibrium moisture content, SEMCmean, can be computed from BOM data

as in Section 2.2.1; or taken the representative value of the hazard zone given in Section 2.2.2.

The constants „1.9‟ and „0.05‟ are the average of „A‟ and „B’ in Table D.4.3.2, which is now

can be taken out as A and B do not vary much with wood types. The simplification led to

Eq.(2.2.3.3) is as in the derivation of the Score System presented in Appendix A.

The maximum and mean seasonal moisture contents of timber in building, BTMmax and

BTMmean, are:

mean mean climate rainBTM TM (2.2.3.4)

max mean max mean mean mean0.1 BTM BTM D TM TM BTM D TM (2.2.3.5)


Tables 4.4.3.2. The adjustment factor for rain (rain) is given in Table 4.4.3.3.

It is noted that compared with the earlier versions of the model (Appendices C and D), we

decided to split the embedded corrosion model into 2 separate parts: one for exposed

structures and one for structures within a building envelope. All model components related to

the building envelope, i.e. roof space, sub-floor, and wall-cavity are therefore taken out of the

model herein. The model for building envelope is developed in Manual No. 9 (Nguyen et.al.

2008b).

Table 2.2.3.1 Mean surface equilibrium moisture content

Hazard zone SEMCmean

A

B

C

9

12

15


Table 2.2.3.2 Damping factor and adjustment factor for climate and micro-climate


Marine

Other

6.0

2.0

2.5

0.5

Table 2.2.3.3 Adjustment factor rain






0

1

3

1

4

9

2

8

17

Note: For corrosion of bolt’s shank (see Section 2.5), this factor is increased by 1.5 times.


2.3.1 Timber Acidity

In this model it will be assumed that the corrosion of untreated timber is related to the acidity

of timber, defined as (7 pH), where pH is the acidity of free water in contact with the wood.

This is a new concept, and is introduced to make the design procedure more widely

applicable. Acidity is used as the basis of the corrosion model since it is the most easily

accessible parameter for corrosion of metal in contact with wood. It can be readily measured,

and in fact measured values are available for a large number of timber species.

A collection of acidity values derived from CSIRO measurements and reports by Davis

(1994) and Bootle (1983) are listed in Table C.2.1, Appendix C. It should be borne in mind

that although the measurement of wood acidity is quick, simple and straightforward it does

show considerable variability from piece to piece, and within the same piece of timber.

2.3.2 Timber Classification

Figure 2.3.1 presents the distribution of the recommended pH values for design of all species

listed in Table C.2.1. From the figure, the acidity classification of timber is established

according to the pH of the species, as defined in Table 2.3.1.


0

5

10

15

20

0 1 2 3 4 5 6 7

pH

Occu

ren

ce f

req

uen

cy

Class

2

Class

3

Class

1

Figure 2.3.1 Histogram of pH values of all species in Table C.2.1 and

Natural Acidity Classification.

Table 2.3.1 Natural acidity classification and representative pH values

Acidity Class Representative pH

value Boundary pH value

1

2

3

5.5

4.5

3.5

5.0

4.0

The species, which were either from Thornton‟s table (Thorton et al. 1997) or TRADAC table

(TRADAC 1999) are listed in Table 2.3.3. The pH value of some species in this list has been

tested and available from Table C.2.1 in Appendix C, and also listed in Table 2.3.3 as

„Measured pH‟.

Figure 2.3.2 shows the Natural Acidity Class versus the density of the tested species divided

into 3 groups: Eucalyptus, Non-Eucalyptus Hardwood and Softwood. The density is seasoned

one determined at 12% moisture content. It can be seen that the acidity class is not in good

correlation with the density of timber.

Therefore, to determine the acidity class of untested species in the list, it is assumed that the

natural acidity class depends on the types of timber, which are divided into Eucalypts, Non-

Eucalypt Hardwoods, and Softwoods. Summary of the simplified classification and

representative pH values for untested species are in Table 2.3.2. Table 2.3.3 presented the

acidity class of timber.

Table 2.3.2 Acidity Classification according to Types of Wood

Type of Wood Acidity Class Representative pH

Eucalypts

Non-Eucalypt Hardwoods

Softwoods

3

2

2

3.5

4.5

4.5


Eucalyptus

0

1

2

3

4

5

6

400 600 800 1000 1200

Density

pH

Eucalyptus

0

1

2

3

4

400 600 800 1000 1200

Density

Natu

ral acid

ity c

lass

Non-Eucalyptus Hardwood

0

1

2

3

4

5

6

400 600 800 1000 1200

Density

pH

Non-Eucalyptus Hardwood

0

1

2

3

4

400 600 800 1000 1200

Density

Natu

ral acid

ity c

lass

Softwood

0

1

2

3

4

5

6

400 600 800 1000 1200

Density

pH

Softwood

0

1

2

3

4

400 600 800 1000 1200

Density

Natu

ral acid

ity c

lass

Figure 2.3.2. Design pH and acidity class versus density of tested species grouped into

Eucalyptus, Non-Eucalyptus Hardwood, and Softwood – Data from Table 2.3.3.


Table 2.3.3 Natural acidity Classification

Standard

Australia

index

Trade name Botanical name Type Density Measured

pH

Natural

acidity

class

22 Ash, alpine Eucalyptus delegatensis E 650 3.6 3

25 Ash, Crow’s Flindersia australis H 950 5.1 1

30 Ash, mountain Eucalyptus regnans E 640 4.7 2

37 Ash, silvertop Eucalyptus sieberi E 862 3.5 3

- Balau (selangan batu) Shorea spp. H 900 - 2

- Bangkirai Shorea laevifolia H 850 - 2

65 Beech, myrtle Nothofagus cunninghamii H 705 - 2

- Belian (ulin) Eusideroxylon zwageri H 1000 - 2

84 Blackbutt Eucalyptus pilularis E 884 3.6 3

86 Blackbutt, New England Eucalyptus andrewsii E 850 - 3

87 Blackbutt, WA Eucalyptus patens E 849 - 3

88 Blackwood Acacia melanoxylon H 650 - 2

97 Bloodwood, red Corymbia gummifera E 900 3.6 3

90 Bloodwood, white Corymbia trachyphloia E 1023 - 3

109 Bollywood Litsea reticulata S 532 3.9 3

121 Box, brush Lophostemon confertus H 900 4.5 2

126 Box, grey Eucalyptus moluccana E 1105 3.5 3

127 Box, grey, coast Eucalyptus bosistoana E 1110 3.4 3

134 Box, long leaved Eucalyptus goniocalyx E 873 - 3

138 Box, red Eucalyptus polyanthemos E 1064 - 3

144 Box, steel Eucalyptus rummeryi E 0 - 3

145 Box, swamp Lophostemon suaveolens H 850 - 2

150 Box, yellow Eucalyptus melliodora E 1075 - 3

148 Box,white Eucalyptus albens E 1112 - 3

162 Brigalow Acacia harpophylla H 1099 - 2

165 Brownbarrel Eucalyptus fastigata E 738 3.3 3

167 Bullich Eucalyptus megacarpa E 640 - 3

- Calantas (kalantas) Toona calantas H 500 - 2

178 Candlebark Eucalyptus rubida E 750 - 3

73 Cedar, red, western Thuja plicata S 448 3.3 3

544 Cypress Callitris glaucophylla S 680 5.4 1

114 Fir, Douglas Pseudotsuga menziesii S 520 3.5 3

253 Gum, blue, southern Eucalyptus globulus E 900 - 3

254 Gum, blue, Sydney Eucalyptus saligna E 843 3.6 3

266 Gum, grey Eucalyptus propinqua E 1050 3.8 3

267 Gum, grey, mountain Eucalyptus cypellocarpa E 961 3.6 3

268 Gum, Maiden's Eucalyptus maidenii E 992 - 3

269 Gum, manna Eucalyptus viminalis E 814 - 3

272 Gum, mountain Eucalyptus dalrympleana E 700 - 3

281 Gum, red, forest Eucalyptus tereticornis E 737 4.2 2

281 Gum, red, river Eucalyptus camaldulensis E 913 - 3

284 Gum, rose Eucalyptus grandis E 753 5.1 1

286 Gum, salmon Eucalyptus salmonophloia E 1070 - 3

288 Gum, scribbly Eucalyptus haemastoma E 907 - 3

289 Gum, shining Eucalyptus nitens E 530 - 3

293 Gum, spotted Corymbia maculata E 988 4.5 2

294 Gum, sugar Eucalyptus cladocalyx E 1105 - 3

305 Gum, yellow Eucalyptus leucoxylon E 1008 - 3

310 Hardwood, Johnstone Backhousia bancroftii H 950 - 2


River

- Hemlock, western Tsuga heterophylla S 500 4.9 2

322 Ironbark, grey Eucalyptus paniculata E 1110 4.0 3

325 Ironbark, red Eucalyptus sideroxylon E 1086 - 3

326 Ironbark, red (broad-

leaved) Eucalyptus fibrosa E 1116 - 3

327 Ironbark, red (narrow-

leaved) Eucalyptus crebra E 1046 4.0 3

336 Ironwood Cooktown Erythrophleum chlorostgchys H 1220 - 2

340 Jam, raspberry Acacia acuminata H 1038 - 2

341 Jarrah Eucalyptus marginata E 823 3.3 3

- Kapur Dryobalanops spp. H 750 3.3 3

344 Karri Eucalyptus diversicolor E 905 4.2 2

Keruing Dipterocarpus spp. H 750 5.1 1

173 Kwila Intsia bijuga H 825 - 2

- Mahogany, Philippine,

red, dark Shorea spp. H 650 - 2


red, light

Shorea, Pentacme,

Parashorea spp. H 550 - 2

384 Mahogany, red Eucalyptus resinifera E 955 3.0 3

391 Mahogany, white Eucalyptus acmenoides E 993 3.5 3

391 Mahogany, white Eucalyptus umbra E 887 - 3

387 Mahonany, southern Eucalyptus botryoides E 919 - 3

411 Mallet, brown Eucalyptus astringens E 974 - 3

432 Marri Corymbia Calophylla E 855 3

- Meranti, red, dark Shorea spp. H 650 3.9 3

- Meranti, red, light Shorea spp. H 400 5.0 2

226 Mersawa (Garawa) Anisoptera thyrifera H 630 4.5 2

434 Messmate Eucalyptus obliqua E 722 3.2 3

435 Messmate, Gympie Eucalyptus cloeziana E 996 - 3

458 Oak, bull Allocasuarina luehmannii H 1050 - 2

240 Oak, white, American Quercus alba H 750 - 2

509 Peppermint, black Eucalyptus amygdalina E 753 - 3

510 Peppermint, broad

leaved Eucalyptus dives E 811 - 3

512 Peppermint, narrow

leaved Eucalyptus radiata E 822 3.2 3

515 Peppermint, river Eucalyptus elata E 804 - 3

529 Pine, black Prumnopitys amara S 500 - 2

533 Pine, caribbean Pinus caribaea S 550 3.9 3

534 Pine, celery-top Phyllocladus asplenifolius S 646 - 2

545 Pine, hoop Araucaria cunninghamii S 550 5.2 1

546 Pine, Huon Lagarostrobos franklinii S 520 4.6 2

548 Pine, kauri Agathis robusta S 503 - 2

549 Pine, King William Athrotaxis selaginoides S 400 - 2

559 Pine, radiata Pinus radiata S 540 4.8 2

561 Pine, slash Pinus elliotii S 650 - 2

- Ramin Gonystylus spp. H 650 5.2 1

326 Redwood Sequoia sempervirens S 400 - 2

332 Rosewood, New Guinea Pterocarpus indicus H 577 - 2

635 Satinay Syncarpia hillii H 838 - 2

668 Stringybark, Blackdown Eucalyptus sphaerocarpa E 1000 - 3

671 Stringybark, brown Eucalyptus capitellata E 838 - 3


676 Stringybark, red Eucalyptus macrorhyncha E 899 - 3

680 Stringybark, white Eucalyptus eugenioides E 856 - 3

681 Stringybark, yellow Eucalyptus muelleriana E 884 4 3

688 Tallowwood Eucalyptus microcorys E 990 3.5 3

- Taun Pometia pinnata H 700 - 2

369 Teak, Burmese Tectona grandis H 600 4.5 2

713 Tingle, red Eucalyptus jacksonii E 772 - 3

714 Tingle, yellow Eucalyptus guilfoylei E 900 - 3

720 Tuart Eucalyptus gomphocephala E 1036 - 3

723 Turpentine Syncarpia glomulifera H 945 3.5 3

747 Wandoo Eucalyptus wandoo E 1099 - 3

774 Woolybutt Eucalyptus longifolia E 1068 - 3

780 Yate Eucalyptus cornuta E 1100 - 3

788 Yertchuk Eucalyptus consideniana E 939 - 3

2.4 Model Equations of Embedded Corrosion

The initial model for embedded corrosion was presented in Appendix C, which was

developed based on a test program of nail‟s embedded corrosion in 120 days provided by

Cole et.al. (internal communication & lab reports). In 2002, based on some expert opinions

from Mackenzie (2000), we modified the model, particularly with reduced 120-day corrosion

for metal embedded in acidity class 3 timber. The modified model in 2002 is presented in

Appendix D.

The final model presented in this section is made with some further simplifications and

modifications to the earlier versions of the model. The simplifications and modifications are

based on

revisiting 120-day corrosion data

calibrating to BRANZ test data (Kear et.al. 2006)

calibrating to 2-year embedded corrosion of nail in-service

Summary of the tests and fittings of the model prediction to the tests‟ data are presented in

Chapter 3.

2.4.1 The Base Model of Embedded corrosion in untreated wood

The corrosion depth of connectors embedded in untreated wood subjected to 120-day

corrosion, f120(M), is:

f120(M) = 0 if M < Mo (2.4.1.1)

f120(M) = 0.2 C120 (M - Mo) if Mo < M < (Mo +5%) (2.4.1.2)

f120(M) = C120 if M (Mo +5) (2.4.1.3)

where M is moisture content. The function is illustrated in Figure 2.4.1.1. Table 2.4.1.1 gives

parameters of the model. Compared to the model in 2002 (Appendix D), the following

revisions have been made, based on a review of data from nails embedded in timber for 120

days and checks with other sources of data (see Chapter 3):

A ramp has put into f120 function from M0 to (M0 +5%)

Parameter M0 for steel in softwood is reduced from 20% to 15%


Parameters C120 are refined and can be estimated from wood pH by the following

linear functions

o For zinc in hardwood,

C120 = 5.0(7.0 pH) 5.5 (2.4.1.4)

o For zinc in softwood,

C120 = (7.0 pH) + 2.5 (2.4.1.5)

o For steel in hardwood,

C120 = 6.0 (7.0 pH) 7.0 (2.4.1.6)

o For steel in softwood,

C120 = 4.0 (7.0 pH) 4.0 (2.4.1.7)

Moisture content

of wood

M (%)

M0

C120

Corrosion depth (m)

f120(M)

In untreated wood

M0 +5%

Figure 2.4.1.1. Base model of embedded corrosion in untreated wood.

Table 2.4.1.1 Parameters of the corrosion model of embedded fasteners in untreated wood

Material Wood type

C120

M0 (%) Acidity

class 1

Acidity

class 2

Acidity

class 3


Softwood 4.0 5.0 6.0 15


Softwood 2.0 6.0 10.0 15

2.4.2 The Base Model of Embedded Corrosion in CCA treated wood

The base model, ie. the model for 120-day corrosion, for both steel and zinc connectors

embedded in CCA treated wood is given by:

f120(M) = 0 if M < 12 (2.4.2.1)

f120(M) = 0.7 (M-12) if M 12 (2.4.2.2)

where M is moisture content. The function is illustrated in Figure 2.4.2.1. Compared to the

2002‟s model (Appendix D), the following revision are made


The same base model are used for steel and zinc

Wood moisture content threshold of the onset of corrosion is revised to 12%


M (%) 12

C120


f120(M)

In CCA treated wood

wood

0.7

Figure 2.4.2.1. Base model of embedded corrosion in CCA-treated wood.

The revision was made to reflect the findings of BRANZ study (Kear et.al. 2006), where steel

corrosion was found consistently higher than zinc corrosion after one year embedded in CCA-

treated wood. The base models used in 2002‟s model (Appendix D), however, contradicted to

this observation. Revisiting the 120-day corrosion data (see Section 3.3), we see that

corrosion of both zinc and steel are more or less at the same rate at 120 days. We therefore

made the revision, ie. using the same base model of zinc and steel in CCA-treated wood. The

fitting of the revised base model to the 120-day data is presented in Section 3.3.

2.4.3 Corrosion Depth

The corrosion depth, c, over the period t years is given by

c = co tn (2.4.3.1)

where co is the corrosion rate (m/year), or more precisely, the corrosion depth for the first

year. For fasteners embedded in untreated wood, n= 0.5 for zinc and n = 0.6 for steel. For

fasteners embedded in CCA-treated wood, n= 0.6 for zinc and n= 1.0 for steel. This revised

long-term effect of CCA-treated wood is based on the understanding that the corrosion

product does not reduce much the corrosion progress caused by chemical agent of CCA in the

treated wood, as it does in untreated wood, particularly for steel.

From the check with data of 2-year corrosion of embedded nail in timber joint exposed to in-

service condition presented in Section 3.1, we found that the 2002‟s model very much over-

predicted the mean measured corrosion (and actually predicted reasonably the worst 10-

percentile of the measured corrosion). The 2002‟s model prediction appeared to be about

twice the mean measured corrosion. For better match with reality, we decided to reduce the

corrosion rate by a factor of 2. The corrosion rate co the becomes

For the case of untreated wood:

o 120 max 120 mean

1( ) 0.3 ( )

2c f BTM f BTM (2.4.3.2)


For the case of treated wood:

For zinc o 120 mean1.3 ( )c f BTM (2.4.3.3)

For steel o 120 mean2.1 ( )c f BTM (2.4.3.4)

where f120 is defined by Eqs. (2.4.1.1) and (2.4.1.2) for untreated wood case and Eqs.(2.4.2.1)

to (2.4.2.2) for CCA treated wood case. It is noted that the corrosion rate of steel is revised to

be approximately 1.6 times the corrosion for zinc. This factor of 1.6 can be derived from

equation (2.4.3.1), and is also supported by BRANZ tests data, as presented in Section 3.2.

The modification for steel corrosion model in treated wood are based on the conclusion of the

BRANZ study, where the zinc coatings were consistently shown to be more durable than mild

steel in all tests. This behaviour, however, was not observed clearly in the 120-day embedded

test as plotted in Figures 3.3.5 and 3.3.6. This was may be due to the duration of test, which

was not long enough for the protective effects of zinc corrosion product to work.

2.5 Design Corrosion Depths

2.5.1 Coefficient of variation

The coefficient of variation of corrosion depths, Vc, is determined from the model predictions

and measurements of corrosion depths given in the fittings/checks in Chapter 3. From the

comparision of the corrosion depths that resulted from the measurement (cm) with the model-

prediction corrosion depths (cp), log-normal distributions are assumed for the uncertainties of

the predicted and measured corrosion depths over time. This leads to the coefficient of

variation of the corrosion depth, denoted by Vc, evaluated as follows (Ang & Tang, 2006),

2

1cV e (2.5.1.1)

in which

2

2 1ln ln

2m pc c

n

(2.5.1.2)

where cm is the measured corrosion depth, cp is the predicted corrosion depth, and n is the

number of data points. The values of Vc thus obtained from the checks with 2-year embedded

nails individual data in Chapter 3. The results are listed in Table 2.5.1.1,

Table 2.5.1.1. Coefficient Vc for embedded corrosion model

Data Group Vc

Marine sites – all steel and zinc 2.6

Non-marine sites – all steel and zinc 1.9

All data, both zinc and steel 2.0

For the Engineering Code, the coefficient Vc for the whole model is set to be 2.0.


2.5.2 Design Corrosion Depths


1design cc c V (2.5.2.1)

where


computed by equations given in Section 2.4.3.

Vc is the coefficient of variation of c, presented in Section 2.5.1.






Refer Manual No.2 (Leicester et.al. 2008) for the derivation of the design corrosion depth.



cb

Corrosion








To compute the corrosion depth due to the embedded corrosion, follow all the steps in

the procedure presented in Chapter 1. To consider the enhancing effect by water ingress

into the bolt‟s hole, the rain factor rain given in Table 1.4.2 is multiplied with a factor of

1.5.


connector is near a beach, see Section 5.4 in Manual No. 5 (Nguyen et.al. 2008a).



It is noted that from calculation results, the corrosion at bolt‟s necks/shanks appeared to be

governed by atmospheric corrosion in most cases. Details of the computed corrosion depth

due to atmospheric corrosion that is enhanced if the connector is near a beach are presented in

Section 5.4 of Manual 5 (Nguyen et.al. 2008a).


3. Data Fittings

3.1 Fittings & calibration with data of 2-year embedded nails exposed to in-service

conditions

The check and calibration of the model is made using data of corrosion on embedded nails,

which were derived from the results of 2-year exposure of nail joints at various locations in 8

houses in VIC, NSW, and QLD (Cole et.al., 1996a, 1996b, 2001, Ganther et.al. , 2000, 2001).

All 8 houses were located in hazard zone C on the embedded corrosion hazard zone map. The

data for Marine climate zone are from the two houses at Harbord (distance to coast = 0.6km)

and Narrabeen (distance to coast = 0.1km). The data for Non-marine climate zone are from

the rest, including the houses at Innisfail 1, Innisfail 2, Mt Buller, Naranderra, Pennant Hills,

and The Gap 18. The nail joints were exposed to 4 microclimates, including outdoor/exterior,

roof space, sub-floor, and wall cavities. Timbers tested are of many species/types, which are

grouped into the following types:

CCA treated pine: includes those described as „Treated pine‟, „H3‟, „H5‟

LOSP treated pine

Eucalypts: Mountain Ash, Spotted Gum

Hardwood: Brush Box

Softwood: Radiata Pine, Douglas Fir

Plywood

The nail joint test specimens consisted of pieces of the timbers 35 mm wide x 20 mm deep x

200 mm long. Each piece had the ends sealed with epoxy resin which was cured before

assembly. There were 4 types of commonly available nails used in the test; hot dip galvanised

41 mm long, zinc plated 31 mm long, blue processed nails 40 mm long and uncoated bright

nails 30 mm long with square copper nails used in some exposures. Processed nails are bright

nails covered with a light polymeric film. The details on nail dimensions are given in Table

3.1.1. The test specimens were constructed by nailing two pieces of each wood along its

length on the 35 mm flat with 3 samples of each type of nail. The separation between each

nail was at least 15 mm, allowing 12 nails per wood type, arranged in two offset lines. Figure

3.1.1 shows the typical nail joint specimen exposed to in-service conditions.


Figure 3.1.1. Exposed nail joint specimens on façade (left) and in subfloor (right)

Table 3.1.1. Nail dimensions

Nail type Section

type

Shank

length (mm)

Diameter

(mm)

Coating

thickness (m)

Shank

surface area

Copper square 29.59 1.94 -- 237

Copper, long square 51.30 2.55 -- 523

Hot dipped round 39.3 2.40 111 296

Zinc Plate round 30.34 1.49 23 142

Process round 40.6 1.90 242

Bright round 28.5 1.94 -- 190

Bright, long round 39.28 1.95 -- 244

The test specimens were exposed for 2 years (or as close to 2 years as practical). Specimens

exposed on the facade of buildings were in general placed approximately 0.4-0.8 metres

below the eaves so that they were sheltered from both direct sunlight and direct rain. If it was

not possible to expose specimens under eaves an artificial shelter was constructed. Specimens

exposed in the sub-floor were generally exposed in a position a significant distance (more

than 2 m) away from any wall and were hung on wire from the floor joists so that they were

midway between joist and earth. Specimens exposed in wall cavities were placed in the cavity

above the sub-floor and thus were in general less than 0.5 m from the bottom of the cavity.

After exposure the nail joint specimens were returned to the laboratory and the nails were

extracted, assessed for extent of corrosion. The corrosion product was removed by cleaning in

acid to determine mass loss of the nails in g/year/m2. One-year-corrosion depth on the nail

shank then can be estimated as follows,

2

2

[g/year/m ] [ m/year] =

[g/m / m]

Mass lossOne year corrosion depth

Density

where the density of zinc is 7.1 g/cm3 (7.1 g/m

2/m), density of steel is 7.7 g/cm

3 (7.7

g/m2/m).


3.1.1 Predictions using the 2002’s model

Figure 3.1.1.1 presents the checks, where the predictions were made by 2002‟s model in

Appendix D. As the result, the predictions overestimate the mean measurement.

0

5

10

15

20

0 5 10 15 20

Predicted corrosion rate (micron/year)

Typ

ical m

easu

red

co

rro

sio

n r

ate

(mic

ron

/year) Bright nail

Hot-dipped

Zinc-plate

0

5

10

15

20

0 5 10 15 20

Predicted corrosion rate (micron/year)T

yp

ical m

easu

red

co

rro

sio

n r

ate

(mic

ron

/year) Bright nail

Hot-dipped

Zinc-plate

Figure 3.1.1.1 Checks with 2-year embedded nails data outdoor using 2002‟s model . Left:

Marine sites, Right: Non-marine sites

3.1.2 Predictions of the nail corrosion in joints exposed outdoor using the current model

Figure 3.1.2.1 presents the checks, where the prediction were made by the final model in

Chapter 1, i.e. with the reduced factor of 2 for the corrosion rate and revised corrosion rate for

steel in CCA-treated timber, as explained in Chapter 2. As the result, the predictions

reasonably agree with the mean measurements. Note that the measured data are group-average

data.

Figure 3.1.2.2 presents the same checks, but using individual measured data. This comparison

between prediction and measurement data is used to estimate the coefficient of variation as

presented in Section 2.5.1. The data are in Table 3.1.2.1 and 3.1.2.2 (Cole, private

communication and internal reports).


Outdoor, Marine

0

5

10

15

0 5 10 15

Predicted corrosion rate

(micron/year)

Ty

pic

al m

ea

su

red

co

rro

sio

n

rate

(m

icro

n/y

ea

r) Bright nail

Hot-dipped

Zinc-plate

Outdoor, Non-marine

0

5

10

15

0 5 10 15


(micron/year)

Typ

ical

measu

red

co

rro

sio

n r

ate

(mic

ron

/year)

Bright nail

Hot-dipped

Zinc-plate

Figure 3.1.2.1 Checks with outdoor 2-year embedded nails group-averaged data using the

current model . Top: Marine sites, Bottom: Non-marine sites


0.0

4.0

8.0

12.0

16.0

20.0

0.00 4.00 8.00 12.00 16.00 20.00

Predicted

Measu

red

Steel

Hot-dipped zinc

Zinc-plated

0.0

4.0

8.0

12.0

0.00 4.00 8.00 12.00

Predicted

Me

asu

red

Steel

Hot-dipped zinc

Zinc-plated

Figure 3.1.2.2 Checks with outdoor 2-year embedded nails individual data using the current

model. Top: Marine sites, Bottom: Non-marine sites


Table 3.1.2.1 Check with individual data of 2-year embedded nails outdoor – Marine sites

SiteSEMC

mean

SEMC

max

Hazard

Zone

Climate

zoneNail Timber

Wood

Type

MassLoss

g/m2/yr

1-year

Corrosion

Depth

(micron)

Prediction

2007

Harbord 15.41 16.227 C Marine bright H3 CCA 3 0.4 6.84

Narrabeen 15.454 16.284 C Marine bright H3 CCA 58 7.5 6.84

Harbord 15.41 16.227 C Marine bright H5 CCA 7 0.9 6.84

Narrabeen 15.454 16.284 C Marine bright H5 CCA 103 13.4 6.84

Narrabeen 15.454 16.284 C Marine bright Treated Pine CCA 90 11.7 6.84

Harbord 15.41 16.227 C Marine bright Mountain Ash E 2 0.3 7.69

Narrabeen 15.454 16.284 C Marine bright Mountain Ash E 61 7.9 7.69

Narrabeen 15.454 16.284 C Marine bright Spotted Gum E 9 1.2 7.69

Narrabeen 15.454 16.284 C Marine bright Brush Box H 21 2.7 4.40

Narrabeen 15.454 16.284 C Marine bright Douglas Fir S 76 9.9 3.30

Narrabeen 15.454 16.284 C Marine bright Radiata Pine S 72 9.4 3.30

Harbord 15.41 16.227 C Marine hot dip H3 CCA 10 1.4 6.84

Narrabeen 15.454 16.284 C Marine hot dip H3 CCA 38 5.4 6.84

Harbord 15.41 16.227 C Marine hot dip H5 CCA 11 1.5 6.84

Narrabeen 15.454 16.284 C Marine hot dip H5 CCA 70 9.9 6.84

Narrabeen 15.454 16.284 C Marine hot dip Treated Pine CCA 122 17.2 6.84

Harbord 15.41 16.227 C Marine hot dip Mountain Ash E 34 4.8 7.80

Narrabeen 15.454 16.284 C Marine hot dip Mountain Ash E 59 8.3 7.80

Narrabeen 15.454 16.284 C Marine hot dip Spotted Gum E 14 2.0 7.80

Narrabeen 15.454 16.284 C Marine hot dip Brush Box H 26 3.7 4.55

Narrabeen 15.454 16.284 C Marine hot dip Douglas Fir S 57 8.0 2.75

Narrabeen 15.454 16.284 C Marine hot dip Radiata Pine S 78 11.0 2.75

Harbord 15.41 16.227 C Marine zinc plate H3 CCA 5 0.7 6.84

Narrabeen 15.454 16.284 C Marine zinc plate H3 CCA 32 4.5 6.84

Harbord 15.41 16.227 C Marine zinc plate H5 CCA 4 0.6 6.84

Narrabeen 15.454 16.284 C Marine zinc plate H5 CCA 48 6.8 6.84

Narrabeen 15.454 16.284 C Marine zinc plate Treated Pine CCA 55 7.7 6.84

Harbord 15.41 16.227 C Marine zinc plate Mountain Ash E 15 2.1 7.80

Narrabeen 15.454 16.284 C Marine zinc plate Mountain Ash E 64 9.0 7.80

Narrabeen 15.454 16.284 C Marine zinc plate Spotted Gum E 4 0.6 7.80

Narrabeen 15.454 16.284 C Marine zinc plate Brush Box H 20 2.8 4.55

Narrabeen 15.454 16.284 C Marine zinc plate Douglas Fir S 29 4.1 2.75

Narrabeen 15.454 16.284 C Marine zinc plate Radiata Pine S 47 6.6 2.75


Table 3.1.2.2 Check with individual data of 2-year embedded nails outdoor – Non-Marine

sites

SiteSEMC-

mean

SEMC-

max

Hazard

Zone

Climate

zoneNail Timber

Wood

Type

Mass

Loss

g/m2/yr

Measured

1-year

Corrosion

Depth

(m)

Model-

Prediction

corrosion

depth

(m)

Innisfail 1 17.3 18.4 C Non-marine bright H3 CCA 3 0.4 3.90


Mt Buller 15.8 19.5 C Non-marine bright H3 CCA 39 5.1 3.90

Naranderra 18.1 22.5 C Non-marine bright H3 CCA 8 1.0 3.90

Pennant Hills 15.0 15.7 C Non-marine bright H3 CCA 4 0.5 3.90



Mt Buller 15.8 19.5 C Non-marine bright H5 CCA 17 2.2 3.90

Naranderra 18.1 22.5 C Non-marine bright H5 CCA 3 0.4 3.90

Pennant Hills 15.0 15.7 C Non-marine bright H5 CCA 8 1.0 3.90

Innisfail 1 17.3 18.4 C Non-marine bright Treated Pine CCA 9 1.2 3.90

Mt Buller 15.8 19.5 C Non-marine bright Treated Pine CCA 60 7.8 3.90

Naranderra 18.1 22.5 C Non-marine bright Treated Pine CCA 8 1.0 3.90

The Gap 18 15.3 16.0 C Non-marine bright Treated Pine CCA 1 0.1 3.90

Innisfail 1 17.3 18.4 C Non-marine bright Mountain Ash E 53 6.9 1.32

Innisfail 2 17.3 18.4 C Non-marine bright Mountain Ash E 72 9.4 1.32

Naranderra 18.1 22.5 C Non-marine bright Mountain Ash E 6 0.8 1.32

Pennant Hills 15.0 15.7 C Non-marine bright Mountain Ash E 1 0.1 1.32

Innisfail 1 17.3 18.4 C Non-marine bright Spotted Gum E 80 10.4 1.32

Innisfail 2 17.3 18.4 C Non-marine bright Spotted Gum E 43 5.6 1.32

Mt Buller 15.8 19.5 C Non-marine bright Spotted Gum E 16 2.1 1.32

Pennant Hills 15.0 15.7 C Non-marine bright Spotted Gum E 0.9 0.1 1.32

The Gap 18 15.3 16.0 C Non-marine bright Spotted Gum E 3 0.4 1.32

Innisfail 1 17.3 18.4 C Non-marine bright Brush Box H 11 1.4 0.75

Innisfail 2 17.3 18.4 C Non-marine bright Brush Box H 15 1.9 0.75

Mt Buller 15.8 19.5 C Non-marine bright Brush Box H 19 2.5 0.75

Naranderra 18.1 22.5 C Non-marine bright Brush Box H 1 0.1 0.75

Pennant Hills 15.0 15.7 C Non-marine bright Brush Box H 10 1.3 0.75

The Gap 18 15.3 16.0 C Non-marine bright Brush Box H 1 0.1 0.75

Innisfail 1 17.3 18.4 C Non-marine bright Douglas Fir S 8 1.0 0.57

Innisfail 2 17.3 18.4 C Non-marine bright Douglas Fir S 16 2.1 0.57

Mt Buller 15.8 19.5 C Non-marine bright Douglas Fir S 27 3.5 0.57

Naranderra 18.1 22.5 C Non-marine bright Douglas Fir S 2 0.3 0.57

Pennant Hills 15.0 15.7 C Non-marine bright Douglas Fir S 2 0.3 0.57

The Gap 18 15.3 16.0 C Non-marine bright Douglas Fir S 2 0.3 0.57

Innisfail 1 17.3 18.4 C Non-marine bright Radiata Pine S 27 3.5 0.57

Innisfail 2 17.3 18.4 C Non-marine bright Radiata Pine S 20 2.6 0.57

Mt Buller 15.8 19.5 C Non-marine bright Radiata Pine S 25 3.2 0.57

Naranderra 18.1 22.5 C Non-marine bright Radiata Pine S 5 0.6 0.57

The Gap 18 15.3 16.0 C Non-marine bright Radiata Pine S 4 0.5 0.57


Table 3.1.2.2 (cont) Check with individual data of 2-year embedded nails outdoor – Non-

Marine sites

SiteSEMC-

mean

SEMC-

max

Hazard

Zone

Climate

zoneNail Timber

Wood

Type

Mass

Loss

g/m2/yr

Measured

1-year

Corrosion

Depth

(m)

Model-

Prediction

corrosion

depth

(m)

Innisfail 1 17.3 18.4 C Non-marine hot dip H3 CCA 14 2.0 2.14


Mt Buller 15.8 19.5 C Non-marine hot dip H3 CCA 41 5.8 2.14

Naranderra 18.1 22.5 C Non-marine hot dip H3 CCA 14 2.0 2.14

Pennant Hills 15.0 15.7 C Non-marine hot dip H3 CCA 12 1.7 2.14



Mt Buller 15.8 19.5 C Non-marine hot dip H5 CCA 30 4.2 2.14

Naranderra 18.1 22.5 C Non-marine hot dip H5 CCA 9 1.3 2.14

Pennant Hills 15.0 15.7 C Non-marine hot dip H5 CCA 7 1.0 2.14

Innisfail 1 17.3 18.4 C Non-marine hot dip Treated Pine CCA 18 2.5 2.14

Mt Buller 15.8 19.5 C Non-marine hot dip Treated Pine CCA 43 6.1 2.14

Naranderra 18.1 22.5 C Non-marine hot dip Treated Pine CCA 15 2.1 2.14

The Gap 18 15.3 16.0 C Non-marine hot dip Treated Pine CCA 7 1.0 2.14

Innisfail 1 17.3 18.4 C Non-marine hot dip Mountain Ash E 45 6.3 5.42

Innisfail 2 17.3 18.4 C Non-marine hot dip Mountain Ash E 53 7.5 5.42

Naranderra 18.1 22.5 C Non-marine hot dip Mountain Ash E 13 1.8 5.42

Pennant Hills 15.0 15.7 C Non-marine hot dip Mountain Ash E 17 2.4 5.42

Innisfail 1 17.3 18.4 C Non-marine hot dip Spotted Gum E 68 9.6 5.42

Innisfail 2 17.3 18.4 C Non-marine hot dip Spotted Gum E 67 9.4 5.42

Mt Buller 15.8 19.5 C Non-marine hot dip Spotted Gum E 27 3.8 5.42

Pennant Hills 15.0 15.7 C Non-marine hot dip Spotted Gum E 5.9 0.8 5.42

The Gap 18 15.3 16.0 C Non-marine hot dip Spotted Gum E 11 1.5 5.42

Innisfail 1 17.3 18.4 C Non-marine hot dip Brush Box H 8 1.1 3.16

Innisfail 2 17.3 18.4 C Non-marine hot dip Brush Box H 15 2.1 3.16

Mt Buller 15.8 19.5 C Non-marine hot dip Brush Box H 7 1.0 3.16

Naranderra 18.1 22.5 C Non-marine hot dip Brush Box H 10 1.4 3.16

Pennant Hills 15.0 15.7 C Non-marine hot dip Brush Box H 14 2.0 3.16

The Gap 18 15.3 16.0 C Non-marine hot dip Brush Box H 5 0.7 3.16

Innisfail 1 17.3 18.4 C Non-marine hot dip Douglas Fir S 25 3.5 0.66

Innisfail 2 17.3 18.4 C Non-marine hot dip Douglas Fir S 21 3.0 0.66

Mt Buller 15.8 19.5 C Non-marine hot dip Douglas Fir S 21 3.0 0.66

Naranderra 18.1 22.5 C Non-marine hot dip Douglas Fir S 3 0.4 0.66

Pennant Hills 15.0 15.7 C Non-marine hot dip Douglas Fir S 6 0.8 0.66

The Gap 18 15.3 16.0 C Non-marine hot dip Douglas Fir S 7 1.0 0.66

Innisfail 1 17.3 18.4 C Non-marine hot dip Radiata Pine S 30 4.2 0.66

Innisfail 2 17.3 18.4 C Non-marine hot dip Radiata Pine S 28 3.9 0.66

Mt Buller 15.8 19.5 C Non-marine hot dip Radiata Pine S 13 1.8 0.66

Naranderra 18.1 22.5 C Non-marine hot dip Radiata Pine S 7 1.0 0.66

The Gap 18 15.3 16.0 C Non-marine hot dip Radiata Pine S 7 1.0 0.66


Table 3.1.2.2 (cont) Check with individual data of 2-year embedded nails outdoor – Non-

Marine sites

SiteSEMC-

mean

SEMC-

max

Hazard

Zone

Climate

zoneNail Timber

Wood

Type

Mass

Loss

g/m2/yr

Measured

1-year

Corrosion

Depth

(m)

Model-

Prediction

corrosion

depth

(m)

Innisfail 1 17.3 18.4 C Non-marine zinc plate H3 CCA 12 1.7 2.14


Mt Buller 15.8 19.5 C Non-marine zinc plate H3 CCA 27 3.8 2.14

Naranderra 18.1 22.5 C Non-marine zinc plate H3 CCA 20 2.8 2.14

Pennant Hills 15.0 15.7 C Non-marine zinc plate H3 CCA 5 0.7 2.14



Mt Buller 15.8 19.5 C Non-marine zinc plate H5 CCA 20 2.8 2.14

Naranderra 18.1 22.5 C Non-marine zinc plate H5 CCA 10 1.4 2.14

Pennant Hills 15.0 15.7 C Non-marine zinc plate H5 CCA 2 0.3 2.14

Innisfail 1 17.3 18.4 C Non-marine zinc plate Treated Pine CCA 8 1.1 2.14

Mt Buller 15.8 19.5 C Non-marine zinc plate Treated Pine CCA 26 3.7 2.14

Naranderra 18.1 22.5 C Non-marine zinc plate Treated Pine CCA 6 0.8 2.14

The Gap 18 15.3 16.0 C Non-marine zinc plate Treated Pine CCA 4 0.6 2.14

Innisfail 1 17.3 18.4 C Non-marine zinc plate Mountain Ash E 57 8.0 5.42

Innisfail 2 17.3 18.4 C Non-marine zinc plate Mountain Ash E 63 8.9 5.42

Naranderra 18.1 22.5 C Non-marine zinc plate Mountain Ash E 7 1.0 5.42

Pennant Hills 15.0 15.7 C Non-marine zinc plate Mountain Ash E 4 0.6 5.42

Innisfail 1 17.3 18.4 C Non-marine zinc plate Spotted Gum E 51 7.2 5.42

Innisfail 2 17.3 18.4 C Non-marine zinc plate Spotted Gum E 50 7.0 5.42

Mt Buller 15.8 19.5 C Non-marine zinc plate Spotted Gum E 12 1.7 5.42

Pennant Hills 15.0 15.7 C Non-marine zinc plate Spotted Gum E 1.6 0.2 5.42

The Gap 18 15.3 16.0 C Non-marine zinc plate Spotted Gum E 7 1.0 5.42

Innisfail 1 17.3 18.4 C Non-marine zinc plate Brush Box H 14 2.0 3.16

Innisfail 2 17.3 18.4 C Non-marine zinc plate Brush Box H 15 2.1 3.16

Mt Buller 15.8 19.5 C Non-marine zinc plate Brush Box H 3 0.4 3.16

Naranderra 18.1 22.5 C Non-marine zinc plate Brush Box H 3 0.4 3.16

Pennant Hills 15.0 15.7 C Non-marine zinc plate Brush Box H 8 1.1 3.16

The Gap 18 15.3 16.0 C Non-marine zinc plate Brush Box H 3 0.4 3.16

Innisfail 1 17.3 18.4 C Non-marine zinc plate Douglas Fir S 6 0.8 0.66

Innisfail 2 17.3 18.4 C Non-marine zinc plate Douglas Fir S 7 1.0 0.66

Mt Buller 15.8 19.5 C Non-marine zinc plate Douglas Fir S 14 2.0 0.66

Naranderra 18.1 22.5 C Non-marine zinc plate Douglas Fir S 2 0.3 0.66

Pennant Hills 15.0 15.7 C Non-marine zinc plate Douglas Fir S 2 0.3 0.66

The Gap 18 15.3 16.0 C Non-marine zinc plate Douglas Fir S 2 0.3 0.66

Innisfail 1 17.3 18.4 C Non-marine zinc plate Radiata Pine S 15 2.1 0.66

Innisfail 2 17.3 18.4 C Non-marine zinc plate Radiata Pine S 8 1.1 0.66

Mt Buller 15.8 19.5 C Non-marine zinc plate Radiata Pine S 23 3.2 0.66

Naranderra 18.1 22.5 C Non-marine zinc plate Radiata Pine S 1 0.1 0.66

The Gap 18 15.3 16.0 C Non-marine zinc plate Radiata Pine S 3 0.42 0.66


3.1.3 Predictions of the nail corrosion in joints within building envelope using the current

model

Figure 3.1.3.1 presents the checks between the measured corrosion rate of nail embedded in

nail joints tested in building envelope parts, including roof space, subfloor and wall cavity,

with the model prediction, which was made by the final model in Chapter 1. The purpose of

this check is to justify the model parameter for building envelope parts (Appendix D) that are

used in the score system (Section 4), which is used in Design Guide (Section 6).

Figure 3.1.3.1 is for the nails in roof-space; Figure 3.1.3.2 is for the nails in sub-floor; Figure

3.1.3.3 is for the nails in wall cavity.

Roofspace, Marine

0

5

10

15

0 5 10 15


(micron/yr)

Typ

ical

measu

red

co

rro

sio

n

rate

(m

icro

n/y

r) Bright nail

Hot-dipped

Zinc-plate

Figure 3.1.2.1 Checks with 2-year embedded nails in roof-space using the current model


Sub-floor, Marine

0

5

10

15

0 5 10 15Predicted corrosion rate

(micron/yr)

Typ

ical

measu

red

co

rro

sio

n

rate

(m

icro

n/y

r) Bright nail

Hot-dipped

Zinc-plate

Sub-floor, Non-marine

0

5

10

15

0 5 10 15

Predicted corrosion rate (micron/yr)

Ty

pic

al m

ea

su

red

co

rro

sio

n

rate

(m

icro

n/y

r) Bright nail

Hot-dipped

Zinc-plate

Figure 3.1.2.1 Checks with outdoor 2-year embedded nails in sub-floor using the current

model . Top: Marine sites, Bottom: Non-marine sites


Wall cavity, Marine

0

5

10

15

0 5 10 15

Predicted corrosion rate (micron/yr)

Typ

ical

measu

red

co

rro

sio

n

rate

(m

icro

n/y

r) Bright nail

Hot-dipped

Zinc-plate

Wall-cavity, Non-marine

0

5

10

15

0 5 10 15Predicted corrosion rate

(micron/yr)

Typ

ical

measu

red

co

rro

sio

n

rate

(m

icro

n/y

r) Bright nail

Hot-dipped

Zinc-plate

Figure 3.1.2.1 Checks with outdoor 2-year embedded nails in wall cavity using the current

model . Top: Marine sites, Bottom: Non-marine sites


3.2 Fitting with data from BRANZ Study Report of Embedded Corrosion Tests

Table 3.2.1 presented the data from in a BRANZ study report by Kear et al. (2006). There

were 2 tests, „Sandwich test‟ and „Panel Pin test‟, where corrosion of mild steel, hot-dipped-

galvanised (HDG) steel, and stainless steel were measured after 12 months (sandwich test) or

14 months (panel pin test) embedded in untreated, CCA-treated, and other preservative-

treated radiata pine timber. The tests were carried out in Lab conditioning rooms with

constant temperature and humidity. The Sandwich test was carried at 21oC and 98% of

relative humidity. The Panel Pin tests were also carried out at 21oC, but at 3 different levels of

relative humidity, including 75%, 90% and 98%, which, as measured and reported in the

study, correspond to average timber moisture contents of 10.5%, 17.9%, and 20.3%,

respectively.

Only data for mild steel and HDG in untreated and CCA-treated timber, which are related to

the model in this report, are presented in Table 3.2.1. The corrosion results were given in

terms of corrosion rate (m/year). Most of the results are determined from the plots in the

BRANZ report, where only few numerical results were given. In Table 3.2.1, it is noted that

the data from Panel Pin test at MC of 20.3% appeared to be inconsistent with the others. The

test gave much higher corrosion rate than the sandwich test did, although they are both

exposed to the same controlled condition, ie. at 21oC and 98% of relative humidity. We think

that at this condition with the configuration of the panel pin tests, it was possible that

condensation could have occurred on the protruding part of the pin and then dripped or

entered by capillary action into the pin hole, resulting in much higher local moisture content

of timber around the pin, and hence higher corrosion rate. The setup of the sandwich test did

not facilitate the condensation, and hence the test results are more reliable. In this section, we

will use the sandwich test results and the panel pin test results at lower MC for calibration,

and neglecting the panel pin test results at the highest MC of 20.3%.

Based on checking and calibrating the model with these data, the most important modification

to the model is for steel corrosion in CCA-treated wood. As a conclusion of the BRANZ

study, the zinc coatings were consistently shown to be more durable than mild steel in all

tests. This behaviour, however, was not observed clearly in the 120-day embedded test as

plotted in Figure C.4.3. To be consistent with the data observed, we re-develop the model for

steel in CCA-treated wood as follows,

The base model for 120-day corrosion of steel and zinc connectors embedded in CCA

treated wood is revised to be the same, see Section 2.4.2. This was due to the duration

of test, which was not long enough for the protective effect of zinc corrosion product

to work.

From Table 3.2.1, the ratio between average corrosion rate of steel and average

corrosion rate of zinc in CCA-treated wood ranges from 1.2 to 2.0, with an average of

1.6. The equation for corrosion rate of steel in CCA-treated wood is then revised to be

1.6 times the corrosion rate of zinc, as presented in Section 2.4.4.

This revision of steel corrosion rate in CCA-treated wood is also consistent with the

equation for corrosion depth over time, Eq.(2.4.3.1), which is

c = co tn (3.2.1)

where n=0.6 for zinc and n=1.0 for steel in treated wood. The corrosion rate is then


o n

cc

t (3.2.2)

Consider the ratio between the corrosion rate of steel and the corrosion rate of zinc:

0.6

0, 0.4

1.0

0,

steel steel steel

zinc zinc zinc

c c t ct

c c t c

(3.3.3)

At t = 1/3 year, ie. 120 days, the corrosion of steel and zinc are the same, then

0.4

0,

0,

11.6

3

steel

zinc

c

c

The ratio is the same as the factor 1.6 obtained from the results of BRANZ test as

presented above.

The comparisons of the model (Section 1) to BRANZ test data are in Figures 3.2.1 to 3.2.4,

which show reasonable agreements.


Zinc in UNTREATED

0

5

10

15

0 10 20 30 40

Timber MC%

Co

rro

sio

n r

ate

(

m/y

ear)

Sandwich-Zinc

Panel Pin-Zinc

CSIROmodel-zinc

Figures 3.2.1 Comparison of the model prediction of corrosion rate (Eq.(1.5.1)) vs timber MC

with BRANZ test data for zinc in untreated Radiata pine (Table 3.2.1)

Steel in UNTREATED

0

5

10

15

0 10 20 30 40

Timber MC%

Co

rro

sio

n r

ate

(

m/y

ear)

Sandwich-Steel

Panel Pin-Steel

CSIROmodel-steel

Figures 3.2.2 Comparison of the model prediction of corrosion rate (Eq.(1.5.1)) vs timber MC

with BRANZ test data of steel in untreated Radiata pine (Table 3.2.1)


Zinc in CCA TREATED

0

10

20

30

0 10 20 30 40

Timber MC%

Co

rro

sio

n r

ate

(

m/y

ear)

Sandwich-Zinc

Panel Pin-Zinc

CSIROmodel-zinc

Figures 3.2.3 Comparison of the model prediction of corrosion rate (Eq.(1.6.1)) vs Timber

MC with BRANZ test data of zinc in treated Radiata pine (Table 3.2.1)

Steel in CCA TREATED

0

10

20

30

0 10 20 30 40

Timber MC%

Co

rro

sio

n r

ate

(

m/y

ear)

Sandwich-Steel

Panel Pin-Steel

CSIROmodel-steel

Figures 3.2.4 Comparison of the model prediction of corrosion rate (Eq.(1.6.2)) vs Timber

MC with BRANZ test data of steel in treated Radiata pine (Table 3.2.1)


Table 3.2.1 Data of corrosion rate of metals from embedded tests in BRANZ Study Report (summarised from Kear et al. 2006)

BRANZ

Tests

Timber

MC %

STEEL corrosion rate (m/y) - Mild steel specimens ZINC corrosion rate (m/y) - HDG steel speciemens

Untreated CCA-treated

Untreated CCA-treated

Avg. H3.2 H4 H5 Avg. H3.2 H4 H5

Sandwich

Test 20.3% 3.4 17.8 13.2 17.2 23.0 3.2 10.8 11.0 10.9 10.4

Panel Pin

Test

20.3% 20.0 66.0 73.0 64.0 61.0 16.0 17.0 10.7 19.0 21.4

17.9% 4.0 3.5 2.2 4.2 4.1 2.0 2.9 1.2 2.0 5.4

10.5% 0.5 1.2 1.1 1.1 1.3 0.5 0.6 0.6 0.3 0.8


3.3 Fitting with 120-day corrosion tests

This is a laboratory test where timber nail-joint specimens were put into conditioned

chambers to investigate the dependency of embedded corrosion on timber moisture contents

for various timber species and/or preservative treatments.

Chambers were established to give a range of constant relative humidity (RH) between 55%

to 100% and a range of temperature (T) between 15°C to 25°C. Salt solutions were used to

regulate RH. When Ca(NO3)2.4H2O, NaNO2, NaNO3, KCl, BaCl2 and K2SO4 salts and

distilled water are used then constant RH of 55, 66, 86, 92, 96 and 100% are established. At a

constant temperature of 20°C, the equilibrium Moisture Content (EMC) of the air is 11, 13,

16, 18, 20, 25, and 30%, respectively. The surface EMC (SEMC) of timber placed in these

chambers can be assumed to reach the air EMC instantly. The air was circulated in the

chambers to ensure that it is well mixed and that condition is uniform.

Timber nail-joint specimens were similar to that of the 2-year exposure test described in

Section 3.1. Timber species were Meranti, Karri, Kauri, Red Ironbark, Oregon, Mountain

Ash, Spotted Gum, BrushBox, Radiata Pine, treated Pine with LOSP, and CCA at H3 and H5

levels. Four types of nail were used, including bright steel, hot-dipped galvanised, zinc-plated,

and copper.

The timbers were put in the chambers, and be weighted once a week. Once their weights do

not change for 3 weeks, they (the whole piece of timber) were considered to reach EMC. Two

sticks of the same species were jointed by a series of nails to make the joint specimens. The

nails were weighted prior to nailing. A minimum of 3 nails for each type will be used for each

timber at each condition. The nail-joint specimens were then left in the chambers for 120

days.

After exposure the nail joint specimens were returned to the laboratory and the nails were

extracted, assessed for extent of corrosion. The corrosion product was removed by cleaning in

acid to determine mass loss of the nails in g/year/m2. One-year-corrosion depth on the nail

shank then can be estimated as follows,

2

2

[g/120days/m ] [ m/120days] =

[g/m / m]

Mass losscorrosion depth

Density

where the density of zinc is 7.1 g/cm3 (7.1 g/m

2/m), density of steel is 7.7 g/cm

3 (7.7

g/m2/m).

The data is presented in Table 3.3.1 (Cole, private communication and internal reports),

which was the same as that used for the base model in 2000 (Appendix C). This section

provides the final check of the data with the current model that has been revised considerably

since 2000. Figures 3.3.1 to 3.3.6 show the check, which justifies the base models presented

in Section 1.


Pine: Radiata, Houn, Kauri (softwood class 2)

0

5

10

15

20

25

0 10 20 30

Timber Moisture Content (%)

Co

rro

sio

n

m/1

20d

ays

Steel

Zinc

Model-steel

Model-zinc

Figures 3.3.1 Check of the model with 120-day corrosion of nails in softwood class 2 timber.

Data from Table 3.3.1. Model Equation is (1.5.2).

Oregon Douglas Fir (softwood class 3)

0

5

10

15

20

25

0 10 20 30


Co

rro

sio

n

m/1

20d

ays

Steel

Zinc

Model-steel

Model-Zinc

Figures 3.3.2 Check of the model with 120-day corrosion of nails in softwood class 3 timber.



Merranti,MA,SP,BB,Karri (Hardwood class 2)

0

5

10

15

20

25

0 10 20 30


Co

rro

sio

n

m/1

20d

ays

Steel

Zinc

Model-steel

Model-zinc

Figures 3.3.3 Check of the model with 120-day corrosion of nails in hardwood class 2 timber.


Red Ironbark (hardwood class 3)

0

5

10

15

20

25

0 10 20 30


Co

rro

sio

n

m/1

20d

ays

Steel

Zinc

Model-steel

Model-zinc

Figures 3.3.4 Check of the model with 120-day corrosion of nails in hardwood class 3 timber.



H3 Treated Radiata

0

5

10

15

20

25

0 10 20 30


Co

rro

sio

n

m/1

20d

ays Steel

Zinc

Model

Figures 3.3.5 Check of the model with 120-day corrosion of nails in H3 CCA-treated Radiata

pine. Data from Table 3.3.1. Model Equation is (1.6.3).

H5 Treated Radiata

0

5

10

15

20

25

0 10 20 30


Co

rro

sio

n

m/1

20d

ays Steel

Zinc

Model

Figures 3.3.6 Check of the model with 120-day corrosion of nails in H5 CCA-treated Radiata

pine. Data from Table 3.3.1. Model Equation is (1.6.3).


Table 3.3.1 Data of 120-day embedded nail corrosion

Timber wood type pH EMC (%)

Bright nail

mass loss

(g/m2 per

120days)

Hot-dip

galvanised

nail mass

loss (g/m2

per

120days)

Steel

corrosion

depth

(micron/

120days)

Zinc

corrosion

depth

(micron/

120days)

Oregon Softwood 4.0 14.5 5 14 0.6 2.0

Oregon Softwood 4.0 15.5 1 24 0.1 3.4

Oregon Softwood 4.0 20.2 33 21 4.3 3.0

Douglas fir Softwood 4.2 10.8 1 13 0.1 1.8

Douglas fir Softwood 4.2 12.3 0.4 9 0.1 1.3






Radiata pine Softwood 5.0 16.8 10 27 1.3 3.8



Radiata pine Softwood 5.0 23.2-90% 7 15 0.9 2.1


Huon Pine Softwood 4.5 14.4 8 16 1.0 2.3



Kauri Softwood 5.1 15.5 2.9 27 0.4 3.8

Kauri Softwood 5.1 22.4 12.5 13 1.6 1.8

Meranti Hardwood 3.9 12.8 8 28 1.0 3.9



Brush box Hardwood 4.4 14 37 36 4.8 5.1

Brush box Hardwood 4.4 17.5 51 47 6.6 6.6

Brush box Hardwood 4.4 21 43 46 5.6 6.5

Karri Eucalyptus 4.0 15.6 43 53 5.6 7.5



Mountain Ash Eucalyptus 4.5 10.8 0.2 12 0.0 1.7

Mountain Ash Eucalyptus 4.5 12.2 1 17 0.1 2.4






Mountain Ash Eucalyptus 4.5 27*-96% 23 24 3.0 3.4

Mountain Ash Eucalyptus 4.5 23.2*-90% 14 26 1.8 3.7


Table 3.3.1 (cont) Data of 120-day embedded nail corrosion

Timber wood type pH EMC (%)

Bright nail

mass loss

(g/m2 per

120days)

Hot-dip

galvanised

nail mass

loss (g/m2

per

120days)

Steel

corrosion

depth

(micron/

120days)

Zinc

corrosion

depth

(micron/

120days)

Red Ironbark Eucalyptus 4.1 15.4 26 140 3.4 19.7



Spotted gum Eucalyptus 4.4 9.9 0 15 0.0 2.1





Spotted gum Eucalyptus 4.4 30

H3 Treated 10.8 0 7 0.0 1.0

H3 Treated 12.5 1.4 13 0.2 1.8

H3 Treated 15 3 29 0.4 4.1

H3 Treated 19.3 29 24 3.8 3.4

H3 Treated 28.0 108 81 14.0 11.4

H3 Treated 24.6* 27 32 3.5 4.5

H5 Treated 12.5 1 21 0.1 3.0

H5 Treated 13.9 1 8 0.1 1.1

H5 Treated 16.7 2 20 0.3 2.8

H5 Treated 20.2 51 35 6.6 4.9

H5 Treated 23.9 41 52 5.3 7.3

H5 Treated 28.7 90 124 11.7 17.5

H5*(8months) Treated 24.4 26 37 3.4 5.2

H5 (8 months) Treated 27 80 108 10.4 15.2

Treated pine Treated 17.2 10 24 1.3 3.4



LOSP Treated 10.4

LOSP Treated 12.2 1 23 0.1 3.2

LOSP Treated 14.7 1 15 0.1 2.1

LOSP Treated 16.6 11 23 1.4 3.2

LOSP Treated 20.8 3 9 0.4 1.3

LOSP Treated 23.2 11 16 1.4 2.3

LOSP Treated 27.2 26 30 3.4 4.2


4. Hazard Score System

4.1 Definition of Hazard Scores

Table 4.1.1 gives the total hazard scores for various scenarios of the corrosion in embedded

fasteners. Derivation of this table is presented in Appendix A. Components of building

envelope, however, are included as they will be present in the Service Life Design Guide.

Table 4.1.1 Hazard scores for corrosion of embedded fasteners

Microclimate

Total scores for various microclimates

Zone A Zone B Zone C

Marine Other Marine Other Marine Other

Subfloor

Wall cavity

Roof space

14

12

11

12

12

9

16

14

13

14

14

11

18

16

15

16

16

13

Outdoors for fasteners other

than bolts

Sheltered / partly sheltered(1)

Exposed vertical surface(2)

Exposed horizontal surface(3)

19

20

22

12

13

15

22

25

30

15

18

23

25

31

40

18

24

33

Outdoors bolts




19

21

24

12

14

17

23

27

35

16

20

28

26

35

49

19

28

42

(1) e.g. house cladding; (2)e.g. fencing; (3) e.g. decking

4.2 Definition of Hazard Class

For ease of application to service life prediction of various types of fastener, the selection of

hazard class limit have been decided to have the same limits for steel and zinc, but to have

different limits for types of wood. The definition of hazard classes and their boundaries in

terms of the total scores for embedded corrosion of fasteners have been chosen as shown in

Table 4.2.1 and illustrated in Figures 4.2.1 and 4.2.2 for zinc and steel fasteners, respectively.

It is noted that there are some revision from the 2002‟s score system (Appendix E), including

Untreated timber is divided into hardwood and softwood only

Expand the range of the middle hazard rating for untreated wood to capture

better the uncertainties around the „jumping‟ step, now is revised as a ramp, of

corrosion with moisture content.


Table 4.2.1 Definition of hazard ratings

Hazard score

Hazard rating In untreated timber

CCA-

treated

timber Hardwoods Softwoods

<12

12~19

>19

na

na

<14

14~22

>22

na

na

<12

12~17

18~23

24~30

>30

HR1emb

HR2emb

HR3emb

HR4emb

HR5emb

Zinc in Eucalypts

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35 40

Total Score

c0

H1 H2 H3

Zinc in Non-Euc. Hardwoods

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35 40

Total Score

c0

H1 H2 H3

Zinc in Softwoods

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35 40

Total Score

c0

H1 H2 H3

Zinc in CCA-treated Woods

0

10

20

30

40

50

0 5 10 15 20 25 30 35 40

Total Score

c0

H1 H2 H3 H4 H5

Figure 4.2.1. Hazard ratings for zinc fasteners embedded in different types of wood

(Data from Appendix B)


Steel in Eucalypts

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35 40

Total Score

c0

H1 H2 H3

Steel in Non-Euc. Hardwoods

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35 40

Total Scorec

0

H1 H2 H3

Steel in Softwoods

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35 40

Total Score

c0

H1 H2 H3

Steel in CCA-treated Woods

0

5

10

15

20

25

30

35

40

45

0 5 10 15 20 25 30 35 40

Total Score

c0

H1 H2 H3 H4 H5

Figure 4.2.2. Hazard ratings for steel fasteners embedded in different types of wood

(Data from Appendix B)

4.3 Derived c0 values for the Score System

Based on the theoretical values of c0 varying in each hazard class, representative values of c0

for the classes are estimated and presented in Tables 4.3.1 and 4.3.2 for zinc and steel,

respectively. Compared to the 2002 model, the assign c0 values for hazard classes are reduced

by a factor about 2, and then the c0 values for steel in CCA treated timber are also revised to

be about 1.6 times those for zinc, as the result from checks and calibration presented in

Section 3.


Table 4.3.1 The first-year corrosion depth of embedded zinc fasteners

Hazard rating

c0 - the first-year corrosion depth of zinc

Untreated timber CCA-treated

timber Acidity Class 1 Acidity Class 2 Acidity Class 3

HR1emb

HR2emb

HR3emb

HR4emb

HR5emb

0

1.0

2.0

na

na

0

2.5

4.5

na

na

0

4.5

8.0

na

na

0

4.0

10.0

15.0

20.0

Table 4.3.2 The first-year corrosion depth of embedded steel fasteners

Hazard rating

c0 - the first-year corrosion depth of steel



HR1emb

HR2emb

HR3emb

HR4emb

HR5emb

0

1.5

3.0

na

na

0

4.5

6.0

na

na

0

7.5

10

na

na

0

7.0

15.0

25.0

32.0

4.4 Corrosion Depth


c = co tn (4.4.1)

where co is the corrosion rate (m/year), or more precisely, the corrosion depth for the first

year. For fasteners embedded in untreated wood, n= 0.5 for zinc and n = 0.6 for steel. For

fasteners embedded in CCA-treated wood, n= 0.6 for zinc and n = 1.0 for steel.

4.5 Service life

The service-life life of a steel fastener is assumed to be the time at which all of the effective

zinc coasting, if any, and 30% of the original strength in steel, is lost. The life of a zinc

coating is assumed to be the time at which all of the effective zinc protection is lost. The

fasteners under consideration are assumed to be subject to bending moment; therefore the

decrease of fastener bending strength is proportional to the increase of corrosion depth. For

conservative calculation, the initial diameter of screws is taken at the root (i.e. excluding the

thread), and that of bolts is taken at the shank.


5. Equations for the Draft Engineering Code

and TimberLife

5.1 Scope and Aplication

This Section provides the calculation procedures for the design corrosion depths on embedded

parts of metal fasteners, which can be used to estimate the corrosion depths for metal

fasteners used in any timber construction located anywhere in Australia.

5.2 Corrosion of Embedded Parts of Fasteners (Embedded Corrosion)

This Section provides the calculation procedures for the design corrosion depths on metal

fasteners‟ parts that are tightly embedded in wood, such as the shank of nails, screws, and

nailplate‟s teeth, as depicted in Figure 5.2.1.

The design corrosion depths is to be determined by

1design cc c V (5.2.1)

where

c is the mean depth of the loss in fastener cross-section due to embedded corrosion for

a chosen design life time. To evaluate the mean corrosion depths, the timber acidity

class and hazard zone of the structure location are obtained from Section 5.2.1. Timber

moisture content is estimated from Section 5.2.2. The mean corrosion depth is then

estimated using the procedure in Section 5.2.3 for fasteners embedded in untreated

wood, and Section 5.2.4 for fasteners embedded in CCA-treated wood.

Vc is the coefficient of variation of c, and is specified parameter related to the target

reliability level. The values of these parameters are set in Section 5.2.5.

Loss of section of embedded steel

c

Figure 5.2. 1 Embedded corrosion depth

5.2.1 Timber Acidity Classification and Hazard zones

Durability classification of timber is listed in Table 3.1.1.


The hazard zone map is shown in Figure 5.2.1.1. Three hazard zones and their representative

mean annual surface equilibrium moisture content SEMCmean and the boundary SEMCmean are

in Table 5.2.1.1. Values of SEMCmean for major cities and towns in Australia are listed in

Table 3.2.1.

Table 5.2.1.1 Effective SEMCmean values for the 3 hazard zones

Zone SEMCmean

A

B

C

9

12

15

Figure 5.2.1.1 Embedded corrosion hazard zone map. Zone C is most hazardous.


5.2.2 Moisture Content of Timber

The mean annual surface equilibrium moisture content, SEMCmean, is given in Table 5.2.1.1,

depending on hazard zones. For a specific location, refer to Table 3.2.1, where the values of

the SEMCmean of major cities and towns in Australia are listed. The mean seasonal moisture

content of a piece of timber, TMmean for one year is estimated as,

TMmean = exp(1.9 + 0.05 SEMCmean) (5.2.2.1)

The mean and maximum seasonal moisture contents of timber in building, BTMmax and

BTMmean, are:

mean mean climate rainBTM TM (5.2.2.2)

max mean mean0.1 BTM BTM D TM (5.2.2.3)


Tables 5.2.2.1. The adjustment factor for rain (rain) is given in Table 5.2.2.2.

Table 5.2.2.1 Damping factor and adjustment factor for climate


Marine*

Other

6.0

2.0

2.5

0.5

* Marine: if the distance to coast < 1 km

Table 5.2.2.2 Adjustment factor rain






0

1

3

1

4

9

2

8

17


5.2.3 Corrosion Depth of embedded fasteners in untreated wood

For the case of untreated wood, corrosion depth for the first year (mm), co is computed as

follows,

o 120 max 120 mean

1( ) 0.3 ( )

2c f BTM f BTM (5.2.3.1)

where f120(M) is the corrosion depth of connectors embedded in untreated wood for 120 days,

given as a function of timber moisture content M,

0

120 120 0 0 0

120 0

0 if ;

( ) 0.2 ( ) if ( +5%);

if ( +5%)

M M

f M C M M M M M

C M M

(5.2.3.2)

The function is illustrated in Figure 5.2.3.1. Values of C120 and M0 are listed in Table 5.2.3.1

depending on the timber acidity class and timber type.

Moisture content

of wood

M (%)

M0

C120

Corrosion depth (m)

f120(M)

In untreated wood

M0 +5%

Figure 5.2.3.1. Base model of embedded corrosion in untreated wood.

Table 5.2.3.1 Parameters of the corrosion model of embedded fasteners in untreated wood

Material Wood type

C120

M0 (%) Acidity

class 1

Acidity

class 2

Acidity

class 3


Softwood 4.0 5.0 6.0 15


Softwood 2.0 6.0 10.0 15

The corrosion depth of embeeded fasteners in untreated wood, c, over the period t years is

computed by

c = co tn (5.2.3.3)



5.2.4 Corrosion Depth of Embedded Fasteners in CCA treated wood

For the case of CCA-treated wood, corrosion depth for the first year (mm), co is computed as

follows,

For Zinc o 120 mean1.3 ( )c f BTM (5.2.4.1)

For steel o 120 mean2.1 ( )c f BTM (5.2.4.2)

where f120(M) is the corrosion depth of connectors embedded in CCA-treated wood for 120

days, given by

0

120

0 0

0 if ;( )

0.7 ( ) if ;

M Mf M

M M M M

(5.2.4.3)

where M is moisture content, M0 = 12%. The function is illustrated in Figure 5.2.4.1.


M (%) 12

C120


f120(M)

In CCA treated wood

wood

0.7

Figure 5.2.4.1. Base model of embedded corrosion in CCA-treated wood.

The corrosion depth of embedded fasteners in CCA-treated wood, c, over the period t years is

computed by

c = co tn (5.2.4.4)



5.2.5 Design Depth of Embedded Corrosion


1design cc c V (5.2.5.1)

where


computed by Eq.(5.2.3.3) or Eq.(5.2.4.4) for a chosen design life time.

Vc is the coefficient of variation of c. From available data, it is recommended that Vc =

2.0.







cb

Corrosion

Figure 5.3.1 Depth of corrosion at the neck of the bolt








To compute the corrosion depth due to the embedded corrosion, follow the procedure in

Section 5.2, with a modification that the adjusted factor rain (Table 5.2.2.2) is

multiplied by factor of 1.5 to take into account the increasing of timber moisture content

due to water ingress into the bolt‟s holes.


connector is near a beach, follow the procedure in Manual No.5.




6. Equations for the Design Guide

6.1 Hazard Zones

Figure 6.1.1. Hazard zone map

6.2 Climate Zones




Timber acidity classification is in Table 6.3.3.


Table 6.3.3 Natural acidity Classification

Standard

Australia

index

Trade name Botanical name Type Density Measured

pH

Natural

acidity

class

22 Ash, alpine Eucalyptus delegatensis E 650 3.6 3

25 Ash, Crow’s Flindersia australis H 950 5.1 1

30 Ash, mountain Eucalyptus regnans E 640 4.7 2

37 Ash, silvertop Eucalyptus sieberi E 862 3.5 3

- Balau (selangan batu) Shorea spp. H 900 - 2

- Bangkirai Shorea laevifolia H 850 - 2

65 Beech, myrtle Nothofagus cunninghamii H 705 - 2

- Belian (ulin) Eusideroxylon zwageri H 1000 - 2

84 Blackbutt Eucalyptus pilularis E 884 3.6 3

86 Blackbutt, New England Eucalyptus andrewsii E 850 - 3

87 Blackbutt, WA Eucalyptus patens E 849 - 3

88 Blackwood Acacia melanoxylon H 650 - 2

97 Bloodwood, red Corymbia gummifera E 900 3.6 3

90 Bloodwood, white Corymbia trachyphloia E 1023 - 3

109 Bollywood Litsea reticulata S 532 3.9 3

121 Box, brush Lophostemon confertus H 900 4.5 2

126 Box, grey Eucalyptus moluccana E 1105 3.5 3

127 Box, grey, coast Eucalyptus bosistoana E 1110 3.4 3

134 Box, long leaved Eucalyptus goniocalyx E 873 - 3

138 Box, red Eucalyptus polyanthemos E 1064 - 3

144 Box, steel Eucalyptus rummeryi E 0 - 3

145 Box, swamp Lophostemon suaveolens H 850 - 2

150 Box, yellow Eucalyptus melliodora E 1075 - 3

148 Box,white Eucalyptus albens E 1112 - 3

162 Brigalow Acacia harpophylla H 1099 - 2

165 Brownbarrel Eucalyptus fastigata E 738 3.3 3

167 Bullich Eucalyptus megacarpa E 640 - 3

- Calantas (kalantas) Toona calantas H 500 - 2

178 Candlebark Eucalyptus rubida E 750 - 3

73 Cedar, red, western Thuja plicata S 448 3.3 3

544 Cypress Callitris glaucophylla S 680 5.4 1

114 Fir, Douglas Pseudotsuga menziesii S 520 3.5 3

253 Gum, blue, southern Eucalyptus globulus E 900 - 3

254 Gum, blue, Sydney Eucalyptus saligna E 843 3.6 3

266 Gum, grey Eucalyptus propinqua E 1050 3.8 3

267 Gum, grey, mountain Eucalyptus cypellocarpa E 961 3.6 3

268 Gum, Maiden's Eucalyptus maidenii E 992 - 3

269 Gum, manna Eucalyptus viminalis E 814 - 3

272 Gum, mountain Eucalyptus dalrympleana E 700 - 3

281 Gum, red, forest Eucalyptus tereticornis E 737 4.2 2

281 Gum, red, river Eucalyptus camaldulensis E 913 - 3

284 Gum, rose Eucalyptus grandis E 753 5.1 1

286 Gum, salmon Eucalyptus salmonophloia E 1070 - 3

288 Gum, scribbly Eucalyptus haemastoma E 907 - 3

289 Gum, shining Eucalyptus nitens E 530 - 3

293 Gum, spotted Corymbia maculata E 988 4.5 2

294 Gum, sugar Eucalyptus cladocalyx E 1105 - 3

305 Gum, yellow Eucalyptus leucoxylon E 1008 - 3

310 Hardwood, Johnstone Backhousia bancroftii H 950 - 2


River

- Hemlock, western Tsuga heterophylla S 500 4.9 2

322 Ironbark, grey Eucalyptus paniculata E 1110 4.0 3

325 Ironbark, red Eucalyptus sideroxylon E 1086 - 3

326 Ironbark, red (broad-

leaved) Eucalyptus fibrosa E 1116 - 3

327 Ironbark, red (narrow-

leaved) Eucalyptus crebra E 1046 4.0 3

336 Ironwood Cooktown Erythrophleum chlorostgchys H 1220 - 2

340 Jam, raspberry Acacia acuminata H 1038 - 2

341 Jarrah Eucalyptus marginata E 823 3.3 3

- Kapur Dryobalanops spp. H 750 3.3 3

344 Karri Eucalyptus diversicolor E 905 4.2 2

Keruing Dipterocarpus spp. H 750 5.1 1

173 Kwila Intsia bijuga H 825 - 2


red, dark Shorea spp. H 650 - 2


red, light

Shorea, Pentacme,

Parashorea spp. H 550 - 2

384 Mahogany, red Eucalyptus resinifera E 955 3.0 3

391 Mahogany, white Eucalyptus acmenoides E 993 3.5 3

391 Mahogany, white Eucalyptus umbra E 887 - 3

387 Mahonany, southern Eucalyptus botryoides E 919 - 3

411 Mallet, brown Eucalyptus astringens E 974 - 3

432 Marri Corymbia Calophylla E 855 3

- Meranti, red, dark Shorea spp. H 650 3.9 3

- Meranti, red, light Shorea spp. H 400 5.0 2

226 Mersawa (Garawa) Anisoptera thyrifera H 630 4.5 2

434 Messmate Eucalyptus obliqua E 722 3.2 3

435 Messmate, Gympie Eucalyptus cloeziana E 996 - 3

458 Oak, bull Allocasuarina luehmannii H 1050 - 2

240 Oak, white, American Quercus alba H 750 - 2

509 Peppermint, black Eucalyptus amygdalina E 753 - 3

510 Peppermint, broad

leaved Eucalyptus dives E 811 - 3

512 Peppermint, narrow

leaved Eucalyptus radiata E 822 3.2 3

515 Peppermint, river Eucalyptus elata E 804 - 3

529 Pine, black Prumnopitys amara S 500 - 2

533 Pine, caribbean Pinus caribaea S 550 3.9 3

534 Pine, celery-top Phyllocladus asplenifolius S 646 - 2

545 Pine, hoop Araucaria cunninghamii S 550 5.2 1

546 Pine, Huon Lagarostrobos franklinii S 520 4.6 2

548 Pine, kauri Agathis robusta S 503 - 2

549 Pine, King William Athrotaxis selaginoides S 400 - 2

559 Pine, radiata Pinus radiata S 540 4.8 2

561 Pine, slash Pinus elliotii S 650 - 2

- Ramin Gonystylus spp. H 650 5.2 1

326 Redwood Sequoia sempervirens S 400 - 2

332 Rosewood, New Guinea Pterocarpus indicus H 577 - 2

635 Satinay Syncarpia hillii H 838 - 2

668 Stringybark, Blackdown Eucalyptus sphaerocarpa E 1000 - 3

671 Stringybark, brown Eucalyptus capitellata E 838 - 3


676 Stringybark, red Eucalyptus macrorhyncha E 899 - 3

680 Stringybark, white Eucalyptus eugenioides E 856 - 3

681 Stringybark, yellow Eucalyptus muelleriana E 884 4 3

688 Tallowwood Eucalyptus microcorys E 990 3.5 3

- Taun Pometia pinnata H 700 - 2

369 Teak, Burmese Tectona grandis H 600 4.5 2

713 Tingle, red Eucalyptus jacksonii E 772 - 3

714 Tingle, yellow Eucalyptus guilfoylei E 900 - 3

720 Tuart Eucalyptus gomphocephala E 1036 - 3

723 Turpentine Syncarpia glomulifera H 945 3.5 3

747 Wandoo Eucalyptus wandoo E 1099 - 3

774 Woolybutt Eucalyptus longifolia E 1068 - 3

780 Yate Eucalyptus cornuta E 1100 - 3

788 Yertchuk Eucalyptus consideniana E 939 - 3


6.4 Total Hazard Scores

Table 6.4.1 gives the total hazard scores for various scenarios of the corrosion in embedded

fasteners.

Table 6.4.1 Hazard scores for corrosion of embedded fasteners

Microclimates

Total Hazard scores



Subfloor

Wall cavity

Roof space

14

12

11

12

12

9

16

14

13

14

14

11

18

16

15

16

16

13

Outdoor:


Vertical surface exposed to rain(2)

Horizontal surface exposed to rain(3)

19

21

24

12

14

17

23

27

35

16

20

28

26

35

49

19

28

42

(1) e.g. house cladding; (2) e.g. fencing, (3) e.g. decking

Note that for the Design Guide, where the Score System is used for estimating the corrosion:

The building envelope parts (roofspace, subfloor and wall cavity) are included with the

assumption that they are reasonably well ventilated.

The total hazard scores used for outdoor were actually those derived for bolts. This is a

conservative assumption as the total hazard scores for other fasteners are slightly lower

than those for bolts.


6.5 Hazard Class

Table 6.5.1 Definition of hazard ratings for fasteners embedded in untreated timber

Hazard score

Hazard rating

Hardwoods Softwoods

<12

12~19

>19

<14

14~22

>22

HR1emb

HR2emb

HR3emb

Table 6.5.2 Definition of hazard ratings for fasteners embedded in CCA-treated timber

Hazard score Hazard rating

<12

12~17

18~23

24~30

>30

HR1emb

HR2emb

HR3emb

HR4emb

HR5emb

6.6 Derived c0 values

Representative values of c0 for the classes are estimated and presented in Tables 6.6.1 and

6.6.2 for zinc and steel, respectively.

Table 6.6.1 The first-year corrosion depth of embedded zinc fasteners

Hazard rating




HR1emb

HR2emb

HR3emb

HR4emb

HR5emb

0

1.0

2.0

na

na

0

2.5

4.5

na

na

0

4.5

8.0

na

na

0

4.0

10.0

15.0

20.0

Table 6.6.2 The first-year corrosion depth of embedded steel fasteners

Hazard rating




HR1emb

HR2emb

HR3emb

HR4emb

HR5emb

0

1.5

3.0

na

na

0

4.5

6.0

na

na

0

7.5

10

na

na

0

7.0

15.0

25.0

32.0


6.7 Corrosion Depth


c = co tn (6.7.1)

where n= 0.5 for zinc and n = 0.6 for steel in untreated timber; n= 0.6 for zinc and n = 1.0 for

steel in CCA-treated timber; co is corrosion depth for the first year (mm)

6.8 Service life









References

Ang AHS, Tang WH. Probability Concepts in Engineering: Emphasis on Applications to

Civil and Environmental Engineering. John Wiley & Sons, 2006.

Bootle, K.R. (1983). Wood in Australia – Types, Properties and Uses, McGraw Hill Book

Co., Sydney, Australia, pp. 62–67.

Cole, I.S., Ganther, W. and Norberg, P. (1996a). Estimation of the Moisture Condition of

Timber Framework in Australian Houses. Proceedings of 25th

Forest Products Research

Conference, CSIRO, Clayton, Australia, 18–21 November, Vol. 1: 10 pages.

Cole, I.S., Ganther, W.D. and Leicester, R.H. (2001). Processes Controlling the Microclimate

in Dwellings on the Eastern Seaboard of Australia. International Conference on Building

Envelope, Ottawa, Canada, 26-29 June 2001.

Cole, I.S., Ganther, W.D., Bradbury, A., & O'Brien, D.J. (1996b) 'Performance of connectors

in treated and untreated Radiata Pine exposed in different parts of the building

envelope', 25th Forest Products Research Conference, Melbourne, Australia, November

18-21, 1996, pp. paper 2/23.

Cole, I.S., Trinidad G.S., and Chan W.Y. (1999), Prediction of the impact of the environment

on timber components: A GIS-based approach, Proc. Durability of Building Materials

and Components 8 (DBMC8), Ottawa, Canada.

Cole, I.S., Private communication and internal data/reports.

David, R. (1994), Timber and Metal – The Connection, Proc. Pacific Engineering

Conference, Gold Coast, Australia, pp. 439–448.

Ganther, W.D., and Cole, I.S. (2000) Factors Controlling the Moisture Content of Timber in

the Building Envelope of Houses in a Number of Climate Zones, Proc. 26th

Forest

Products Research Conference, Clayton VIC, Australia

Ganther, W.D., Cole, I.S., and Leicester, R.H. (2001). Measurement of Microclimate in

Dwellings Along the Australian Eastern Seaboard. International Conference on

Building Envelope, Ottawa, Canada, 26-29 June 2001.

Kear G., Wu H-Z, and Jones MS. (2006). „The Corrosion of Metallic Fastener Materials in

Untreated, CCA-, CuAz-, and ACQ-based Timbers‟, BRANZ Study Report No. SR 153.

BRANZ Ltd, Judgeford, New Zealand.

Leicester, R.H, Foliente, G.C., Wang, C-H., Nguyen, M.N., Seath, C.A. and MacKenzie, C.,

(2002) Timber Durability Compendium, BCE Doc 02/062, CSIRO Building,

Construction & Engineering, Highett, Victoria, March.

Leicester, R.H., Ganther, W.D., Seath, S.A., Wang, C-H., Nguyen, M.N., Foliente, G.C. and

Cole, I.S. (2004). “Australian Houses: Monitoring and Predicting Microclimate and the

Durability of the Building Envelope,” Proceedings of the Conference on Woodframe

Housing Durability and Disaster Issues, Las Vegas, Nevada, USA, 4–6 October 2004.


Leicester, R.H., Nguyen, M.N., and Wang, C-H. (2008) “Manual No. 2: Derivation of design

Equations for Use with AS1720.1.”, CSIRO Sustainable Ecosystems, available online at

Forest & Wood Products Australia website: www.fwpa.com.au.

Mackenzie, C. Private Communications

Nguyen, M.N., Leicester, R.H. and Wang, C-H. (2008a) “Manual No. 5: Atmospheric

corrosion of fasteners in timber structures.” CSIRO Sustainable Ecosystems, available

online at Forest & Wood Products Australia website: www.fwpa.com.au.

Nguyen, M.N., Leicester, R.H. and Wang, C-H. (2008b) “Manual No. 9: Service Life Models

for Timber Structure protected in Building Envelopes” CSIRO Sustainable Ecosystems,

available online at Forest & Wood Products Australia website: www.fwpa.com.au.

Siau , J.F. (1995) Wood: Influence of Moisture on Physical Properties. Dept of Wood Science

and Forest Products, Virginia Polytechnic Institute and State University, 1995,

227 pages.

Thornton, J.D., Johnson, G.C., and Nguyen, N-K. (1997). Revised CSIRO Natural Durability

Classification – In-ground Durability Ratings for Mature Outer Heartwood, CSIRO

Forestry and Forest Products, Clayton, Victoria, June.

TRADAC (1999). Species, Properties and Uses, Technical Data Sheet 16, Timber Research

& Development Advisory Council of Queensland, Brisbane, QLD.

Wang, C-H., and Leicester, R.H. (2008) “Manual No. 1: Processed Climate Data for Timber

Service Life Prediction Modelling”, CSIRO Sustainable Ecosystems, available online at

Forest & Wood Products Australia website: www.fwpa.com.au.

http://www.fwpa.com.au/





APPENDIX A

Derivation of Score System to Estimate Timber Moisture Content

This section presents the development of the score system based on the model equations in

Appendix D for estimating the maximum moisture content of timber in buildings (BTMmax).

Further simplifications of the simplified theory presented in Appendix D are needed to

establish a simple linear score system to predict the moisture content of wood, as follows.

From Eqs. (D.4.3.1), (D.4.3.2), and (D.4.3.3), we get

TMmax = exp(2B) TMmean (A.1)

Consider the factor „exp(2B)‟ with B values from Table D.4.3.2

For hardwoods B = 0.050 then exp(2B) = 1.105

For softwoods B = 0.054 then exp(2B) = 1.114

For CCA-treated pine B = 0.045 then exp(2B) = 1.094

It can be seen that the factor „exp(2B)‟ does not change much, and has the average of 1.1.

Then approximately we have

TMmax = 1.1 TMmean (A.2)

Using Eqs.(A.2) and (2.4.3.4), Eq.(D.4.3.5) can be divided into 4 terms as follows,

max mean mean microclimate climate rain0.1 ( ) BTM TM D TM (A.3)

The 1st term TMmean depends mainly on hazard zone. Average values and variation range of

TMmean for untreated wood are listed in Table A.1, from which the score for hazard zones,

Scorehazard-zone, are set.

The 2nd

term depends mainly on the damping parameter D. The total average value of TMmean

(calculated for all possible cases – see Appendix B) is 11.8. Therefore, the 2nd

term can be

approximated as 1.2D. The score for the effects of this „damping term‟, Scoredamping, can be

determined as shown in Table A.2, where D values are from Table D.4.3.3.

The 3rd

and the 4th

terms can be used together to establish the score for microclimate,

Scoreclimate, due to climate effects. The two terms Δclimate and Δmicroclimate can be simply

summed together to give the score.


The last term Δrain gives the score for rain effects, Scorerain, as given in Table A.4. Values of

Δrain are from Table D.4.3.4. For bolts, as presented in Section 1.8, the scores are 1.5 times

higher than those for other fasteners.

The total score is calculated as

Scoretotal = Scorehazard-zone + Scoredamping + Scoreclimate+ Scorerain (A.4)

With the way to establish the score system as presented above, the total score Scoretotal is also

the estimate of the maximum moisture content of wood in building (BTMmax). Figure A.1

shows the total score Scoretotal versus the BTMmax calculated by the timber moisture content

model in Section 1.2.2 for all possible combinations of climates at different hazard and

climate zones for different types of wood (see Appendix B). It can be seen that the score

approximates the moisture content quite well. The errors between BTMmax and the total score

are also shown in Table B.1, Appendix B. In all cases, the errors are quite small.

Table A.1 Scores for Hazard Zones determined from the term TMmean in Eq. (A.3)

Hazard zones Average of TMmean Variation range of

TMmean Scoreharzard-zone

A

B

C

9.8

11.4

13.3

9.6~9.9

11.3~11.5

13.3

9

11

13

Table A.2 Scores for microclimate determined by damping factor D

Microclimate

D

(from Table D.4.3.3) Scoredamping 1.2 D

Marine Other Marine Other

Sub-floor

Wall cavity

Roof space

Facades (Outdoor)

2.0

1.5

2.0

6.0

1.0

1.5

2.0

2.0

2.5

2.0

2.5

7.5

1.5

2.0

2.5

2.5

Table A.3 Scores for microclimate determined by climate adjusted factors

Microclimate Scoreclimate =

Δclimate + Δmicroclimate

Marine Other

Sub-floor

Wall cavity

Roof space

Outdoor:

2.5

0.5

-0.5

2.5

1.5

1.0

-2.5

0.5


Table A.4 Scores for the effect of rain determined by the rain adjustment factor

Outdoor (Facades)

Microclimate

Scorerain = rain


For fasteners other than bolts




0

1

3

1

4

9

2

8

17

For bolts




0

1.5

4.5

1.5

6

13.5

3

12

25.5

Table A.5 Total scores for corrosion of embedded fasteners calculated by Eq.(A.4)

Microclimate

Total scores for various microclimates



Subfloor

Wall cavity

Roof space

14

12

11

12

12

9

16

14

13

14

14

11

18

16

15

16

16

13

Outdoors for fasteners other

than bolts

Sheltered / partly sheltered

Exposed vertical surface

Exposed horizontal surface

19

20

22

12

13

15

22

25

30

15

18

23

25

31

40

18

24

33

Outdoors bolts

Sheltered / partly sheltered

Exposed vertical surface

Exposed horizontal surface

19

21

24

12

14

17

23

27

35

16

20

28

26

35

49

19

28

42


0.0

10.0

20.0

30.0

40.0

50.0

0 10 20 30 40 50

Total Score (Score total )

BT

Mm

ax

Figure A.1. Maximum moisture content of timber in buildings (BTMmax) versus

total score (Scoretotal) – Data is from Table B.1, Appendix B.


APPENDIX B

MOISTURE CONTENTS & FIRST-YEAR CORROSION DEPTHS

FOR THEORETICAL CORROSION SCENARIOS

Table B.1 presents the calculation of timber moisture contents and the first-year corrosion

depths for all possible corrosion scenarios, which are made by combinations of different

microclimates with different hazard and climate zones for different types of wood in the

Timber Moisture content model in Section 1.2.2.

The total score determined by Eq.(A.4) to estimate the maximum moisture content of timber

in building as present in Section 4 is also provided. The error of the estimation is computed as

max

max

100

Total score BTMerror

BTM

(%) (C.1)


Table B.1 Calculation of moisture contents and the first-year corrosion depths of all theoretical corrosion scenarios Hazard

Zone

SEMC

mean

SEMC

max rain

Wood

typeA B C120 M0 Micro-climate

Climate

ZoneD

climate

micro

TMmean TMmax BTMmean BTMmaxTotal

score

Error*

%

A 9 11 0 E 1.9 0.05 14 15 Subfloor Marine 2.0 2.0 0.5 10.49 11.59 12.99 15.19 14 -7.8

A 9 11 0 E 1.9 0.05 14 15 Subfloor Other 1.0 0.0 1.5 10.49 11.59 11.99 13.09 12 -8.3

A 9 11 0 E 1.9 0.05 14 15 Wall Marine 1.5 2.0 -1.5 10.49 11.59 10.99 12.64 11.5 -9.0

A 9 11 0 E 1.9 0.05 14 15 Wall Other 1.5 0.0 1.0 10.49 11.59 11.49 13.14 12 -8.7

A 9 11 0 E 1.9 0.05 14 15 Roof Marine 2.0 2.0 -2.5 10.49 11.59 9.99 12.19 11 -9.8

A 9 11 0 E 1.9 0.05 14 15 Roof Other 2.0 0.0 -2.5 10.49 11.59 7.99 10.19 9 -11.7

A 9 11 0 E 1.9 0.05 14 15 Outdoor no rain Marine 6.0 2.0 0.5 10.49 11.59 12.99 19.60 19 -3.1

A 9 11 0 E 1.9 0.05 14 15 Outdoor no rain Other 2.0 0.0 0.5 10.49 11.59 10.99 13.19 12 -9.0

A 9 11 1 E 1.9 0.05 14 15 Outdoor+rainV Marine 6.0 2.0 0.5 10.49 11.59 13.99 20.60 20 -2.9

A 9 11 1 E 1.9 0.05 14 15 Outdoor+rainV Other 2.0 0.0 0.5 10.49 11.59 11.99 14.19 13 -8.4

A 9 11 3 E 1.9 0.05 14 15 Outdoor+rainH Marine 6.0 2.0 0.5 10.49 11.59 15.99 22.60 22 -2.7

A 9 11 3 E 1.9 0.05 14 15 Outdoor+rainH Other 2.0 0.0 0.5 10.49 11.59 13.99 16.19 15 -7.4

A 9 11 0 H 1.9 0.05 8 15 Subfloor Marine 2.0 2.0 0.5 10.49 11.59 12.99 15.19 14 -7.8

A 9 11 0 H 1.9 0.05 8 15 Subfloor Other 1.0 0.0 1.5 10.49 11.59 11.99 13.09 12 -8.3

A 9 11 0 H 1.9 0.05 8 15 Wall Marine 1.5 2.0 -1.5 10.49 11.59 10.99 12.64 11.5 -9.0

A 9 11 0 H 1.9 0.05 8 15 Wall Other 1.5 0.0 1.0 10.49 11.59 11.49 13.14 12 -8.7

A 9 11 0 H 1.9 0.05 8 15 Roof Marine 2.0 2.0 -2.5 10.49 11.59 9.99 12.19 11 -9.8

A 9 11 0 H 1.9 0.05 8 15 Roof Other 2.0 0.0 -2.5 10.49 11.59 7.99 10.19 9 -11.7

A 9 11 0 H 1.9 0.05 8 15 Outdoor no rain Marine 6.0 2.0 0.5 10.49 11.59 12.99 19.60 19 -3.1

A 9 11 0 H 1.9 0.05 8 15 Outdoor no rain Other 2.0 0.0 0.5 10.49 11.59 10.99 13.19 12 -9.0

A 9 11 1 H 1.9 0.05 8 15 Outdoor+rainV Marine 6.0 2.0 0.5 10.49 11.59 13.99 20.60 20 -2.9

A 9 11 1 H 1.9 0.05 8 15 Outdoor+rainV Other 2.0 0.0 0.5 10.49 11.59 11.99 14.19 13 -8.4

A 9 11 3 H 1.9 0.05 8 15 Outdoor+rainH Marine 6.0 2.0 0.5 10.49 11.59 15.99 22.60 22 -2.7

A 9 11 3 H 1.9 0.05 8 15 Outdoor+rainH Other 2.0 0.0 0.5 10.49 11.59 13.99 16.19 15 -7.4

A 9 11 0 S 1.9 0.05 6 15 Subfloor Marine 2.0 2.0 0.5 10.49 11.59 12.99 15.19 14 -7.8

A 9 11 0 S 1.9 0.05 6 15 Subfloor Other 1.0 0.0 1.5 10.49 11.59 11.99 13.09 12 -8.3

A 9 11 0 S 1.9 0.05 6 15 Wall Marine 1.5 2.0 -1.5 10.49 11.59 10.99 12.64 11.5 -9.0

A 9 11 0 S 1.9 0.05 6 15 Wall Other 1.5 0.0 1.0 10.49 11.59 11.49 13.14 12 -8.7

A 9 11 0 S 1.9 0.05 6 15 Roof Marine 2.0 2.0 -2.5 10.49 11.59 9.99 12.19 11 -9.8

A 9 11 0 S 1.9 0.05 6 15 Roof Other 2.0 0.0 -2.5 10.49 11.59 7.99 10.19 9 -11.7

A 9 11 0 S 1.9 0.05 6 15 Outdoor no rain Marine 6.0 2.0 0.5 10.49 11.59 12.99 19.60 19 -3.1

A 9 11 0 S 1.9 0.05 6 15 Outdoor no rain Other 2.0 0.0 0.5 10.49 11.59 10.99 13.19 12 -9.0

A 9 11 1 S 1.9 0.05 6 15 Outdoor+rainV Marine 6.0 2.0 0.5 10.49 11.59 13.99 20.60 20 -2.9

A 9 11 1 S 1.9 0.05 6 15 Outdoor+rainV Other 2.0 0.0 0.5 10.49 11.59 11.99 14.19 13 -8.4

A 9 11 3 S 1.9 0.05 6 15 Outdoor+rainH Marine 6.0 2.0 0.5 10.49 11.59 15.99 22.60 22 -2.7

A 9 11 3 S 1.9 0.05 6 15 Outdoor+rainH Other 2.0 0.0 0.5 10.49 11.59 13.99 16.19 15 -7.4

A 9 11 0 CCA 1.9 0.05 0 12 Subfloor Marine 2.0 2.0 0.5 10.49 11.59 12.99 15.19 14 -7.8

A 9 11 0 CCA 1.9 0.05 0 12 Subfloor Other 1.0 0.0 1.5 10.49 11.59 11.99 13.09 12 -8.3

A 9 11 0 CCA 1.9 0.05 0 12 Wall Marine 1.5 2.0 -1.5 10.49 11.59 10.99 12.64 11.5 -9.0

A 9 11 0 CCA 1.9 0.05 0 12 Wall Other 1.5 0.0 1.0 10.49 11.59 11.49 13.14 12 -8.7

A 9 11 0 CCA 1.9 0.05 0 12 Roof Marine 2.0 2.0 -2.5 10.49 11.59 9.99 12.19 11 -9.8

A 9 11 0 CCA 1.9 0.05 0 12 Roof Other 2.0 0.0 -2.5 10.49 11.59 7.99 10.19 9 -11.7

A 9 11 0 CCA 1.9 0.05 0 12 Outdoor no rain Marine 6.0 2.0 0.5 10.49 11.59 12.99 19.60 19 -3.1

A 9 11 0 CCA 1.9 0.05 0 12 Outdoor no rain Other 2.0 0.0 0.5 10.49 11.59 10.99 13.19 12 -9.0

A 9 11 1 CCA 1.9 0.05 0 12 Outdoor+rainV Marine 6.0 2.0 0.5 10.49 11.59 13.99 20.60 20 -2.9

A 9 11 1 CCA 1.9 0.05 0 12 Outdoor+rainV Other 2.0 0.0 0.5 10.49 11.59 11.99 14.19 13 -8.4

A 9 11 3 CCA 1.9 0.05 0 12 Outdoor+rainH Marine 6.0 2.0 0.5 10.49 11.59 15.99 22.60 22 -2.7

A 9 11 3 CCA 1.9 0.05 0 12 Outdoor+rainH Other 2.0 0.0 0.5 10.49 11.59 13.99 16.19 15 -7.4


Hazard

Zone

SEMC

mean

SEMC

max rain

Wood


Climate

ZoneD

climate

micro


score

Error*

%

B 12 14 0 E 1.9 0.05 14 15 Subfloor Marine 2.0 2.0 0.5 12.18 13.46 14.68 17.24 16 -7.2

B 12 14 0 E 1.9 0.05 14 15 Subfloor Other 1.0 0.0 1.5 12.18 13.46 13.68 14.96 14 -6.4

B 12 14 0 E 1.9 0.05 14 15 Wall Marine 1.5 2.0 -1.5 12.18 13.46 12.68 14.60 13.5 -7.6

B 12 14 0 E 1.9 0.05 14 15 Wall Other 1.5 0.0 1.0 12.18 13.46 13.18 15.10 14 -7.3

B 12 14 0 E 1.9 0.05 14 15 Roof Marine 2.0 2.0 -2.5 12.18 13.46 11.68 14.24 13 -8.7

B 12 14 0 E 1.9 0.05 14 15 Roof Other 2.0 0.0 -2.5 12.18 13.46 9.68 12.24 11 -10.2

B 12 14 1 E 1.9 0.05 14 15 Outdoor no rain Marine 6.0 2.0 0.5 12.18 13.46 15.68 23.37 22 -5.9

B 12 14 1 E 1.9 0.05 14 15 Outdoor no rain Other 2.0 0.0 0.5 12.18 13.46 13.68 16.24 15 -7.7

B 12 14 4 E 1.9 0.05 14 15 Outdoor+rainV Marine 6.0 2.0 0.5 12.18 13.46 18.68 26.37 25 -5.2

B 12 14 4 E 1.9 0.05 14 15 Outdoor+rainV Other 2.0 0.0 0.5 12.18 13.46 16.68 19.24 18 -6.5

B 12 14 9 E 1.9 0.05 14 15 Outdoor+rainH Marine 6.0 2.0 0.5 12.18 13.46 23.68 31.37 30 -4.4

B 12 14 9 E 1.9 0.05 14 15 Outdoor+rainH Other 2.0 0.0 0.5 12.18 13.46 21.68 24.24 23 -5.1

B 12 14 0 H 1.9 0.05 8 15 Subfloor Marine 2.0 2.0 0.5 12.18 13.46 14.68 17.24 16 -7.2

B 12 14 0 H 1.9 0.05 8 15 Subfloor Other 1.0 0.0 1.5 12.18 13.46 13.68 14.96 14 -6.4

B 12 14 0 H 1.9 0.05 8 15 Wall Marine 1.5 2.0 -1.5 12.18 13.46 12.68 14.60 13.5 -7.6

B 12 14 0 H 1.9 0.05 8 15 Wall Other 1.5 0.0 1.0 12.18 13.46 13.18 15.10 14 -7.3

B 12 14 0 H 1.9 0.05 8 15 Roof Marine 2.0 2.0 -2.5 12.18 13.46 11.68 14.24 13 -8.7

B 12 14 0 H 1.9 0.05 8 15 Roof Other 2.0 0.0 -2.5 12.18 13.46 9.68 12.24 11 -10.2

B 12 14 1 H 1.9 0.05 8 15 Outdoor no rain Marine 6.0 2.0 0.5 12.18 13.46 15.68 23.37 22 -5.9

B 12 14 1 H 1.9 0.05 8 15 Outdoor no rain Other 2.0 0.0 0.5 12.18 13.46 13.68 16.24 15 -7.7

B 12 14 4 H 1.9 0.05 8 15 Outdoor+rainV Marine 6.0 2.0 0.5 12.18 13.46 18.68 26.37 25 -5.2

B 12 14 4 H 1.9 0.05 8 15 Outdoor+rainV Other 2.0 0.0 0.5 12.18 13.46 16.68 19.24 18 -6.5

B 12 14 9 H 1.9 0.05 8 15 Outdoor+rainH Marine 6.0 2.0 0.5 12.18 13.46 23.68 31.37 30 -4.4

B 12 14 9 H 1.9 0.05 8 15 Outdoor+rainH Other 2.0 0.0 0.5 12.18 13.46 21.68 24.24 23 -5.1

B 12 14 0 S 1.9 0.05 6 15 Subfloor Marine 2.0 2.0 0.5 12.18 13.46 14.68 17.24 16 -7.2

B 12 14 0 S 1.9 0.05 6 15 Subfloor Other 1.0 0.0 1.5 12.18 13.46 13.68 14.96 14 -6.4

B 12 14 0 S 1.9 0.05 6 15 Wall Marine 1.5 2.0 -1.5 12.18 13.46 12.68 14.60 13.5 -7.6

B 12 14 0 S 1.9 0.05 6 15 Wall Other 1.5 0.0 1.0 12.18 13.46 13.18 15.10 14 -7.3

B 12 14 0 S 1.9 0.05 6 15 Roof Marine 2.0 2.0 -2.5 12.18 13.46 11.68 14.24 13 -8.7

B 12 14 0 S 1.9 0.05 6 15 Roof Other 2.0 0.0 -2.5 12.18 13.46 9.68 12.24 11 -10.2

B 12 14 1 S 1.9 0.05 6 15 Outdoor no rain Marine 6.0 2.0 0.5 12.18 13.46 15.68 23.37 22 -5.9

B 12 14 1 S 1.9 0.05 6 15 Outdoor no rain Other 2.0 0.0 0.5 12.18 13.46 13.68 16.24 15 -7.7

B 12 14 4 S 1.9 0.05 6 15 Outdoor+rainV Marine 6.0 2.0 0.5 12.18 13.46 18.68 26.37 25 -5.2

B 12 14 4 S 1.9 0.05 6 15 Outdoor+rainV Other 2.0 0.0 0.5 12.18 13.46 16.68 19.24 18 -6.5

B 12 14 9 S 1.9 0.05 6 15 Outdoor+rainH Marine 6.0 2.0 0.5 12.18 13.46 23.68 31.37 30 -4.4

B 12 14 9 S 1.9 0.05 6 15 Outdoor+rainH Other 2.0 0.0 0.5 12.18 13.46 21.68 24.24 23 -5.1

B 12 14 0 CCA 1.9 0.05 0 12 Subfloor Marine 2.0 2.0 0.5 12.18 13.46 14.68 17.24 16 -7.2

B 12 14 0 CCA 1.9 0.05 0 12 Subfloor Other 1.0 0.0 1.5 12.18 13.46 13.68 14.96 14 -6.4

B 12 14 0 CCA 1.9 0.05 0 12 Wall Marine 1.5 2.0 -1.5 12.18 13.46 12.68 14.60 13.5 -7.6

B 12 14 0 CCA 1.9 0.05 0 12 Wall Other 1.5 0.0 1.0 12.18 13.46 13.18 15.10 14 -7.3

B 12 14 0 CCA 1.9 0.05 0 12 Roof Marine 2.0 2.0 -2.5 12.18 13.46 11.68 14.24 13 -8.7

B 12 14 0 CCA 1.9 0.05 0 12 Roof Other 2.0 0.0 -2.5 12.18 13.46 9.68 12.24 11 -10.2

B 12 14 1 CCA 1.9 0.05 0 12 Outdoor no rain Marine 6.0 2.0 0.5 12.18 13.46 15.68 23.37 22 -5.9

B 12 14 1 CCA 1.9 0.05 0 12 Outdoor no rain Other 2.0 0.0 0.5 12.18 13.46 13.68 16.24 15 -7.7

B 12 14 4 CCA 1.9 0.05 0 12 Outdoor+rainV Marine 6.0 2.0 0.5 12.18 13.46 18.68 26.37 25 -5.2

B 12 14 4 CCA 1.9 0.05 0 12 Outdoor+rainV Other 2.0 0.0 0.5 12.18 13.46 16.68 19.24 18 -6.5

B 12 14 9 CCA 1.9 0.05 0 12 Outdoor+rainH Marine 6.0 2.0 0.5 12.18 13.46 23.68 31.37 30 -4.4

B 12 14 9 CCA 1.9 0.05 0 12 Outdoor+rainH Other 2.0 0.0 0.5 12.18 13.46 21.68 24.24 23 -5.1


Hazard

Zone

SEMC

mean

SEMC

max rain

Wood


Climate

ZoneD

climate

micro


score

Error*

%

C 15 17 0 E 1.9 0.05 14 15 Subfloor Marine 2.0 2.0 0.5 14.15 15.64 16.65 19.63 18 -8.3

C 15 17 0 E 1.9 0.05 14 15 Subfloor Other 1.0 0.0 1.5 14.15 15.64 15.65 17.14 16 -6.7

C 15 17 0 E 1.9 0.05 14 15 Wall Marine 1.5 2.0 -1.5 14.15 15.64 14.65 16.89 15.5 -8.2

C 15 17 0 E 1.9 0.05 14 15 Wall Other 1.5 0.0 1.0 14.15 15.64 15.15 17.39 16 -8.0

C 15 17 0 E 1.9 0.05 14 15 Roof Marine 2.0 2.0 -2.5 14.15 15.64 13.65 16.63 15 -9.8

C 15 17 0 E 1.9 0.05 14 15 Roof Other 2.0 0.0 -2.5 14.15 15.64 11.65 14.63 13 -11.1

C 15 17 2 E 1.9 0.05 14 15 Outdoor no rain Marine 6.0 2.0 0.5 14.15 15.64 18.65 27.59 25 -9.4

C 15 17 2 E 1.9 0.05 14 15 Outdoor no rain Other 2.0 0.0 0.5 14.15 15.64 16.65 19.63 18 -8.3

C 15 17 8 E 1.9 0.05 14 15 Outdoor+rainV Marine 6.0 2.0 0.5 14.15 15.64 24.65 33.59 31 -7.7

C 15 17 8 E 1.9 0.05 14 15 Outdoor+rainV Other 2.0 0.0 0.5 14.15 15.64 22.65 25.63 24 -6.4

C 15 17 17 E 1.9 0.05 14 15 Outdoor+rainH Marine 6.0 2.0 0.5 14.15 15.64 33.65 42.59 40 -6.1

C 15 17 17 E 1.9 0.05 14 15 Outdoor+rainH Other 2.0 0.0 0.5 14.15 15.64 31.65 34.63 33 -4.7

C 15 17 0 H 1.9 0.05 8 15 Subfloor Marine 2.0 2.0 0.5 14.15 15.64 16.65 19.63 18 -8.3

C 15 17 0 H 1.9 0.05 8 15 Subfloor Other 1.0 0.0 1.5 14.15 15.64 15.65 17.14 16 -6.7

C 15 17 0 H 1.9 0.05 8 15 Wall Marine 1.5 2.0 -1.5 14.15 15.64 14.65 16.89 15.5 -8.2

C 15 17 0 H 1.9 0.05 8 15 Wall Other 1.5 0.0 1.0 14.15 15.64 15.15 17.39 16 -8.0

C 15 17 0 H 1.9 0.05 8 15 Roof Marine 2.0 2.0 -2.5 14.15 15.64 13.65 16.63 15 -9.8

C 15 17 0 H 1.9 0.05 8 15 Roof Other 2.0 0.0 -2.5 14.15 15.64 11.65 14.63 13 -11.1

C 15 17 2 H 1.9 0.05 8 15 Outdoor no rain Marine 6.0 2.0 0.5 14.15 15.64 18.65 27.59 25 -9.4

C 15 17 2 H 1.9 0.05 8 15 Outdoor no rain Other 2.0 0.0 0.5 14.15 15.64 16.65 19.63 18 -8.3

C 15 17 8 H 1.9 0.05 8 15 Outdoor+rainV Marine 6.0 2.0 0.5 14.15 15.64 24.65 33.59 31 -7.7

C 15 17 8 H 1.9 0.05 8 15 Outdoor+rainV Other 2.0 0.0 0.5 14.15 15.64 22.65 25.63 24 -6.4

C 15 17 17 H 1.9 0.05 8 15 Outdoor+rainH Marine 6.0 2.0 0.5 14.15 15.64 33.65 42.59 40 -6.1

C 15 17 17 H 1.9 0.05 8 15 Outdoor+rainH Other 2.0 0.0 0.5 14.15 15.64 31.65 34.63 33 -4.7

C 15 17 0 S 1.9 0.05 6 15 Subfloor Marine 2.0 2.0 0.5 14.15 15.64 16.65 19.63 18 -8.3

C 15 17 0 S 1.9 0.05 6 15 Subfloor Other 1.0 0.0 1.5 14.15 15.64 15.65 17.14 16 -6.7

C 15 17 0 S 1.9 0.05 6 15 Wall Marine 1.5 2.0 -1.5 14.15 15.64 14.65 16.89 15.5 -8.2

C 15 17 0 S 1.9 0.05 6 15 Wall Other 1.5 0.0 1.0 14.15 15.64 15.15 17.39 16 -8.0

C 15 17 0 S 1.9 0.05 6 15 Roof Marine 2.0 2.0 -2.5 14.15 15.64 13.65 16.63 15 -9.8

C 15 17 0 S 1.9 0.05 6 15 Roof Other 2.0 0.0 -2.5 14.15 15.64 11.65 14.63 13 -11.1

C 15 17 2 S 1.9 0.05 6 15 Outdoor no rain Marine 6.0 2.0 0.5 14.15 15.64 18.65 27.59 25 -9.4

C 15 17 2 S 1.9 0.05 6 15 Outdoor no rain Other 2.0 0.0 0.5 14.15 15.64 16.65 19.63 18 -8.3

C 15 17 8 S 1.9 0.05 6 15 Outdoor+rainV Marine 6.0 2.0 0.5 14.15 15.64 24.65 33.59 31 -7.7

C 15 17 8 S 1.9 0.05 6 15 Outdoor+rainV Other 2.0 0.0 0.5 14.15 15.64 22.65 25.63 24 -6.4

C 15 17 17 S 1.9 0.05 6 15 Outdoor+rainH Marine 6.0 2.0 0.5 14.15 15.64 33.65 42.59 40 -6.1

C 15 17 17 S 1.9 0.05 6 15 Outdoor+rainH Other 2.0 0.0 0.5 14.15 15.64 31.65 34.63 33 -4.7

C 15 17 0 CCA 1.9 0.05 0 12 Subfloor Marine 2.0 2.0 0.5 14.15 15.64 16.65 19.63 18 -8.3

C 15 17 0 CCA 1.9 0.05 0 12 Subfloor Other 1.0 0.0 1.5 14.15 15.64 15.65 17.14 16 -6.7

C 15 17 0 CCA 1.9 0.05 0 12 Wall Marine 1.5 2.0 -1.5 14.15 15.64 14.65 16.89 15.5 -8.2

C 15 17 0 CCA 1.9 0.05 0 12 Wall Other 1.5 0.0 1.0 14.15 15.64 15.15 17.39 16 -8.0

C 15 17 0 CCA 1.9 0.05 0 12 Roof Marine 2.0 2.0 -2.5 14.15 15.64 13.65 16.63 15 -9.8

C 15 17 0 CCA 1.9 0.05 0 12 Roof Other 2.0 0.0 -2.5 14.15 15.64 11.65 14.63 13 -11.1

C 15 17 2 CCA 1.9 0.05 0 12 Outdoor no rain Marine 6.0 2.0 0.5 14.15 15.64 18.65 27.59 25 -9.4

C 15 17 2 CCA 1.9 0.05 0 12 Outdoor no rain Other 2.0 0.0 0.5 14.15 15.64 16.65 19.63 18 -8.3

C 15 17 8 CCA 1.9 0.05 0 12 Outdoor+rainV Marine 6.0 2.0 0.5 14.15 15.64 24.65 33.59 31 -7.7

C 15 17 8 CCA 1.9 0.05 0 12 Outdoor+rainV Other 2.0 0.0 0.5 14.15 15.64 22.65 25.63 24 -6.4

C 15 17 17 CCA 1.9 0.05 0 12 Outdoor+rainH Marine 6.0 2.0 0.5 14.15 15.64 33.65 42.59 40 -6.1

C 15 17 17 CCA 1.9 0.05 0 12 Outdoor+rainH Other 2.0 0.0 0.5 14.15 15.64 31.65 34.63 33 -4.7

CSE 79

Appendix C:. Model Equations 2000

C.1. Introduction

This section presents the early version of the model (Cole, private communication / internal

reports) for corrosion of both hot-dipped zinc and bright steel fasteners, which are embedded

in untreated and CCA-treated timbers. The model for embedded corrosion uses wood acidity

as a starting point. Seasonal moisture content of the wood is used as the corroding parameter

indicator.

C.2 Timber Acidity

In this model it will be assumed that the corrosion of untreated timber is related to the acidity

of timber, defined as (7 pH), where pH is the acidity of free water in contact with the wood.

This is a new concept, and is introduced to make the design procedure more widely

applicable. Acidity is used as the basis of the corrosion model since it is the most easily

accessible parameter for corrosion of metal in contact with wood. It can be readily measured,

and in fact measured values are available for a large number of timber species.

A collection of acidity values derived from BCE measurements and reports by Davis (1994)

and Bootle (1983) are reported in Table C.2.1. It should be borne in mind that although the

measurement of wood acidity is quick, simple and straightforward it does show considerable

variability from piece to piece, and within the same piece of timber.

Table C.2.1. Reported pH values of timber species

Common Name Botanical Name BCE Bootle Davis

Suggested

Design

pH

Alder, brown Caldcluvia paniculosa 5.0 5.0

Ash, Alpine Eucalyptus delegatensis 3.6 3.6

Ash, Crow's Flindersia australis 5.1 5.1

Ash, English Fraxinus excelsoir 3.5-5.3 4.0

Ash, Silver Flindersia bourjotiana 5.1 5.1

Ash, Silvertop Eucalyptus sieberi 3.5 3.5

Ash, mountain Eucalyptus regnans 4.7 4.7

Balsa Ochroma pyramidale 5.4-7.2 6.0

Baltic, red Pinus sylvestris 4.3-4.6 4.5

Baltic, white 4.0-5.0 4.5

Bangalay 3.56 3.6

Bean, black Castanospermum australe 3.8-5.2 4.2

Beech Fagus spp? 4.5-5.9 5.0

Beech, European Fagus sylvatica 4.5-6.1 5.0

CSE 80


Suggested

Design

pH

Beech, negrohead Nothofagus moorei 4.6-5.1 5.0

Beech, silky Citronella moorie 5.7 5.7

Beech, white Gmelina dairympleana 4.6-5.0 4.8

Birch, white Schizomeria ovata 3.9-4.9 4.2

Blackbutt Eucalyptus pilularis 4.69 3.4 3.12-3.25 3.6

Bloodwood, red Eucalyptus gummifera 3.6 3.6

Bollywood Cinnamomum baileyanum 3.9 3.9

Box, grey Eucalyptus microcarpa 3.5 3.5

Coastal grey box Eucalyptus bosistoana 3.43 3.4

Brownbarrel Eucalyptus fastigata 3.3 3.3

Brush box Tristania conferta 4.6 3.9-4.6 4.55 4.5

Carabeen, yellow Sloanea woollsii 4.4 4.4

P. Caribae Pinus caribaea 5.31 5.3

Cedar, red, western Thuja plicata 2.9-4.0 2.9-4.7 3.3

Chestnut Castanea sativa 3.6 3.6

Coachwood Ceratopetalum apetalum 5.0 5.0

Cypress Cupressus macrocarpa 5.35 5.4

Elm Ulmus spp 6.0-7.2 6.0-7.2 6.2

Fir, Douglas Pseudotsuga menziesii 4.0 3.1-4.4 3.5

Douglas Fir, Oregon Pine Pseudotsuga menziesii 3.1-4.4 3.5

Geronggang 2.6 2.6

Gum, grey Eucalyptus canaliculata 3.8 3.8

Forest red gum Eucalyptus blakelyi 4.96 3.7 4.2

Rose gum Eucalyptus grandis 5.12 5.1

Mountain grey gum Eucalyptus cypellocarpa 3.57 3.6

Sydney Blue gum Eucalyptus saligna 3.6-4.2 3.65-3.80 3.6

Flooded gum Eucalyptus rudis 3.84 3.8

Spotted gum Eucalyptus citriodora 4.5 46-5.0 4.25-4.68 4.5

Hemlock, western Tsuga heterophylla 4.8-5.4 4.9

Hickory Carya spp 5.2 5.2

Iroko Chlorophora excelsa 5.2-7.2 5.5

Red ironbark Eucalyptus crebra 5.06 3.7 3.66 4.0

4.1 4.0

Grey ironbark Eucalyptus drepanophylla 5.82 3.7 4.88 4.0

Jarrah Eucalyptus marginata 3.0-3.7 3.0-3.7 3.3

Jelutong Dyera costulata 4.6 4.65 4.6

Kapur (Camphorwood) Cinnamomum oliveri 3.2-3.7 3.3

Karri Eucalyptus diversicolor 4.3 4.1 4.05 4.2

Kauri Agathis vitiensis 5.2 5.2

Kempas 3.6-4.6 4.0

Keruing Dipterocarpus genus 5.1 5.1

Larch, European Larix decidua 4.0 4.0

Lignum vitae Guaiacum officinale 3.6 3.6

LOSP 4.6 4.6

Mahogany, African Khaya ivorensis 4.5-5.1 4.7

Mahogany, brush Geissois benthamii 5.1 5.1

Mahogany, red Eucalyptus pellita 2.4-3.4 3.0

Mahogany, rose Dysoxylum fraseranum 4.0 4.0

Mahogany, white Eucalyptus acmenoides 3.9 3.24 3.5

Cuban mahogany Swietenia spp 2.75 2.7

CSE 81


Suggested

Design

pH

(sapwood)

(heartwood) 3.85 3.8

Maple, rose Cryptocarya erythroxylon 5.5 5.5

Maple, sugar Queensland? Flindersia brayleyana 5.0-5.8 5.4

Meranti Shorea spp 3.9 3.9

Meranti, red, light Shorea spp 4.3-6.1 5.2 5.0

Meranti, red, dark

(sapwood) Shorea spp 3.9-5.3 5.4 5.0

(heartwood) 3.85 3.9

Mercau Merbau? Pometia acuminata 4.3 4.3

Mersawa Anisoptera sp 4.3-4.6 4.5

Messmate Eucalyptus obliqua 3.2 3.2

Oak, European Quercus ilex 3.3-5.2 4.0

Oak, Japanese Quercus mongolica 3.2-4.7 3.8

Southern Silky Oak Grevilla robusta 4.95 4.9

Oregon Pseudotsuga taxifolia 3.9 3.9

Peppermint Eucalyptus radiata 3.15 3.2

Pine, cypress, white Callitris columellaris 5.7 5.7

Pine, hoop Araucaria cunninghamii 5.2 5.2

Pine, maritime Pinus pinaster 3.8 3.8 3.8

Pine, radiata Pinus radiata 5.0 4.0-4.8 4.8

Pine, Huon Dacrydium franklinii 4.6 4.6

Pine, caribbean Pinus caribaea 3.9 3.9

Pine, scots Pinus sylvestris 4.3-4.6 4.5

Poplar Populus spp 4.6-5.6 5.0

Ramin 5.2 5.25 5.2

Sacau (Fiji) 5.58 5.6

Sapote Calocarpus sapota 5.3-4.6 5.0

Sassafras Daphnandra dielsii 5.5 5.5

Seraya, white Shorea spp 5.0-5.5 5.3

Spruce, Sitka Oicea sitchensis 3.4-5.5 4.0

Sycamore Acer pseudoplatanus 4.3-6.0 5.0

Tallowwood Eucalyptus microcorys 3.6-3.8 3.55-3.56 3.5

Teak Tectona grandis 4.5 4.5

Turpentine Syncarpia glomulifera 3.6-3.9 3.21 3.5

Yellow stringybark Eucalyptus muellerana 4.73 3.62 4.0

Yellowwood Flindersia xanthoxyla 4.9-5.2 5.0

H3, CCA treated Radiata

pine 4.8 na

H5, CCA treated Radiata

pine 4.9 na

CSE 82

C.3. Corrosion Model

C.3.1 The Base Corrosion Model

The base models was developed based on corrosion data of metals embedded in untreated and

treated timber at moisture content M for 120 days (Cole, internal reports – see Section 3.3).

The base models are shown in Figures (C.3.1) and (C.3.2) respectively. Specifically, the

metals herein refer to hot dipped galvanised zinc and bright steel. The corrosion depth at 120

days, denoted as f120(M) on the vertical axis is a function of the moisture content of the

timber. For untreated wood, under constant conditions, the corrosion is defined by a threshold

moisture content Mo. For values of M < Mo, f120(M) = 0; For values of M Mo, f120(M) = C120.

For treated wood, the corrosion depth is defined by a threshold moisture content Mo, and a

value of f120(M) that increase with the moisture content of the timber, M.

C.3.2 Parameters for Untreated Wood

For the case of connectors embedded in untreated wood, at constant moisture content over

120 days, the following equations are proposed; C120, in m is the depth of corrosion.

The corrosion model for connectors embedded in untreated wood subjected to 120 days

corrosion is then:

f120(M) = 0 if M < Mo (C.3.1)

f120(M) = C120 if M Mo (C.3.2)

where Mo and C120 are defined as follows by equations (C.3.3) to (C.3.10).

For zinc in hardwood, C120 = 0.150 exp{1.62 (7 pH)} (C.3.3)

For zinc in softwood, C120 = 3.19 exp{0.179 (7 pH)} (C.3.4)

For steel in hardwood, C120 = 0.120 exp{1.74 (7 pH)} (C.3.5)

For steel in softwood, C120 = 0.280 exp{1.19 (7 pH)} (C.3.6)

Where the value of pH used are given in Table C.2.1. The moisture threshold parameters Mo

(%) are set as follows:

For zinc in hardwood, Mo = 10 (C.3.7)

For zinc in softwood, Mo = 15 (C.3.8)

For steel in hardwood, Mo = 15 (C.3.9)

For steel in softwood, Mo = 20 (C.3.10)

The fit of the proposed model with the test data for various species is shown in Section C.4. It

is seen that the fit is reasonably good except for the case of Meranti species.

C.3.3 Parameters for CCA-Treated Wood

The model for of zinc connectors embedded in CCA treated wood is given by:

f120(M) = 0 if M < Mo (C.3.11)

f120(M) = 0.7 (M-10) if M Mo (C.3.12)

CSE 83

where Mo = 10

The model for of steel connectors embedded in CCA treated wood is given by:

f120(M) = 0 if M < Mo (C.3.13)

f120(M) = 0.7 (M-13) if M Mo (C.3.14)

where Mo = 13

C.3.4 Moisture Content of Timber

Before the corrosion depth for an embedded fastener can be computed using the base models,

the moisture content of the timber, appropriate to the climate and microclimate must first be

calculated. A model for moisture content of timber was developed based on a test program

presented in Cole et.al., 1996a, 1999, Ganther et.al. , 2000.

Initially, the surface equilibrium moisture content (SEMC) for a given temperature and

humidity is calculated according to Bramhall‟s equation as follows:

ee 2

e

log ( /100) 0.0251log

17.884 0.0002362( 273) 0.1432( 273)

0.92 log 1.0327 0.000674( 273)

H

T TSEMC

T

(C.3.15)

where



The SEMC should be calculated every three hours, using data from a nearby Bureau of

Meteorology station. The three hourly data should then be averaged for each of the four

seasons, beginning with summer (i.e. December to February) to obtain values for each of the

four seasons, SEMCseason (i.e. SEMCsummer, SEMCautumn, SEMCwinter , SEMCspring). We assume

that the seasonal value of SEMC penetrates reasonably deep into the timber. From these four

values, we can compute SEMCmean, the mean annual value of the four seasonal moisture

contents, and SEMCmax, the maximum seasonal SEMC. Both of these values are required in

the embedded corrosion procedure, and can be derived from Bureau of Meteorology station

data. Alternatively, values of SEMCmean can be obtained from published maps in a variety of

sources, including some Australian Standards. A map of SEMCmean for Australia is shown in

Figure C.3.3. If maps of SEMCmax are not available, then for practical purposes, SEMCmax can

be computed directly from Bureau of Meteorology data or approximated as

(SEMCmean + 2) %. From these values, the moisture content of the timber can be calculated for

various exposure conditions. Let us define the following notation for the moisture content in a

piece of timber:

TM – the seasonal value of moisture content in a piece of timber

TMmax – the maximum value out of the four TM values for one year

CSE 84

TMmean – the mean annual value of the four TM values for one year

The moisture content for a season of the exposed timber, TMseason, can be calculated using the

following:

season seasonexp TM A B SEMC (C.3.16)

where A and B are given in Table C.3.2. TM is then calculated for each of the seasons, using

the seasonal SEMC values and subsequently TMmax and TMmean are calculated. Finally, these

values are used to calculate the maximum and mean values of the moisture content in the

timber within the building of interest, by adjusting for the microclimate in the following

manner.

Let us define the following notation for timber inside a building:

BTM – the seasonal value of moisture content of timber in a building

BTMmax – the maximum value out of the four BTM values for one year

BTMmean – the mean annual value of the four BTM values for one year.

The moisture content of the timber in the building, BTM, can be calculated using the

following:

max mean max mean microclimate climateBTM TM D TM TM (C.3.17)

mean mean microclimate climateBTM TM (C.3.18)

The damping factor (D) and the adjustment factors for the climate (climate) and the

microclimate (microclimate) are given in Tables C.3.3 and C.3.4.

In Tables C.3.3 and C.3.4, the damping, climate and microclimate depend on a climate zone

classification of the building location. To derive this zone classification, the building location

is first defined in terms of a climate type according to Figure C.3.4, and then the step-by-step

procedure specified in Table C.3.5 is used to derive the climate zone.

C.3.5 Computation of Corrosion Depth

Now that the moisture content of the timber for the appropriate climate and microclimate has

been calculated, the corrosion depth, over a period of time can be computed.


c = co tn (C.3.19)

where n= 0.5 for zinc and n = 0.6 for steel; co is corrosion depth for the first year.


o 120 max 120 mean( ) 0.3 ( ) c f BTM f BTM (C.3.20)

CSE 85

For the case of CCA-treated wood:

o 120 mean2.5 ( )c f BTM (C.3.21)

where f120 is defined by equations (C.3.1) to (C.3.14). The form of Eqs. (C.3.19) to (C.3.21) is

developed in Cole (internal reports).

Table C.3.2. Moisture content parameters A and B

Moisture Content

Parameter Hardwoods Softwoods CCA Treated Pine

A 1.84 1.78 2

B 0.05 0.054 0.045

Table C.3.3. Damping factor used in calculation of BTM

Climate Zone Damping, D

Sub-Floor Wall-cavity Roof-space Facades

TROPICAL 1.5 1.5 1.5 1

SUB-TROPICAL 1 1.5 2 1.5

TEMPERATE 1 1.5 2 3

INLAND 0.5 0.6 0.6 1

ALPINE 0.2 0.6 0.6 1

MARINE 2 1.5 2 6

Table C.3.4. Climate and Micro-climate adjustment factors used in calculation of BTM

Climate Zone climate microclimate

Sub-Floor Wall-

cavity

Roof-space Facades

TROPICAL 0 1.5 2 -4.5 0.5

SUB-TROPICAL 0 0.5 0.5 -5.0 0.5

TEMPERATE 0 0.5 0.5 -4.5 0.5

INLAND 0 0.5 0.5 -2.5 0.5

ALPINE 1 1.5 -0.5 -2.5 0.5

MARINE 2 0.5 -1.5 -2.5 0.5

CSE 86

Table C.3.5. Definition of Climate Zone

Step 1. First: determine the climate type from the map in Figure C.3.4.

Step 2. Check if in MARINE Zone

If the distance to the coast < 1km then zone = MARINE

Step 3. Check if in ALPINE Zone

If the distance to the coast >1km

If climate type is temperate and elevation > 700m then zone = ALPINE

If climate type is tropical and elevation > 300m then zone = ALPINE

If climate type is sub-tropical and elevation > 250m then zone = ALPINE

Step 4. Check if in INLAND Zone

If the distance to the coast > 100 km

If climate type is sub-tropical–arid then zone = INLAND

If climate type is temperate –arid then zone = INLAND

Step 5. If not MARINE, ALPINE or INLAND, then:

If climate type is tropical then zone = TROPICAL

If climate type is sub-tropical then zone = SUBTROPICAL

If climate type is temperate then zone = TEMPERATE

CSE 87

C 120

Moisture content of wood (%)

Corrosion function f120(M) 12

0 (

M 0

Figure C.3.1. Corrosion function f120(M) for timber embedded in untreated wood.

Moisture content of wood (%)

C orrosion function

f120(M)

M 0

Figure C.3.2. Corrosion function f120(M) for timber embedded in CCA treated wood.

CSE 88

Figure 1.3.3. Annual mean surface moisture content of timber outdoors.

Cairns

Brisbane

Sydney

Canberra Albury

Melbourne

Hobart

Adelaide

Dubbo

Perth

Dalby

Darwin

Onslow Alice Springs

Mount Isa

10

10

10

11

11

11

12

12

12

12

12

15

15

1

5

15

14 14

13

9

9 9

9

11

16

13 13

14 13

13 14

13

CSE 89

Figure C.3.4. Climate Type, used to derive Climate Zone by the procedure in Table C.3.5

CSE 90

C.4 Data from nails embedded in timber for 120 days under constant moisture content

The data on nails embedded in timber for 120 days has been given in Section 3.3. This

Section provides the fitting of the data with the early version of the model presnted in this

appendix. The fitting function f120 in Section C.3 for the hot dipped galvanised zinc and for

bright steel are compared with the measured data. Data is shown in Figure C.4.1 for nails

embedded in hardwoods, in Figure C.4.2 for nails embedded in softwoods and in Figure C.4.3

for nails embedded in CCA treated timber. It is to be noted that the model predictions are

reasonably good for all cases except for the case of Meranti timber. This may be due to the

fact that Meranti is the trade name given to a mixture of more than 50 tropical species of

timber, and that quite different species may have been used in the measurements of acidity

and the nail corrosion rate. Data is in Table 3.3.1.

CSE 91

Figure C.4.1. Comparison of corrosion model for embedded metal,

with test data for hardwoods.

CSE 92

Figure C.4.1 (cont) Comparison of corrosion model for embedded metal,


CSE 93

MERANTI

0

5

10

15

20

25

30

0 10 20 30

Moisture content (%)

Co

rro

sio

n (

m /

12

0 d

ay

s)

Bright

Hot dip

zinc

Model

steel

model



CSE 94

DOUGLAS FIR

0

5

10

15

20

0 10 20 30 40

moisture content (%)

co

rro

sio

n [

gm

/m2/1

20 d

ays]

steel

zinc

Steel model

Zinc model

Figure C.4.2 Comparison of corrosion model for embedded metal,

with test data for softwood timber.

CSE 95

KAURI PINE

0

5

10

15

20

25

0 10 20 30


Co

rro

sio

n (

m /

12

0 d

ay

s)

Bright

Hot dip

zinc

Model

steel

model

LOSP TREATED SOFTWOOD

0

5

10

15

20

25

0 10 20 30


Co

rro

sio

n (

m /

12

0 d

ay

s)

Bright

Hot dip

zinc

Model

steel

model



CSE 96

HUON PINE

0

5

10

15

20

25

0 10 20 30


Co

rro

sio

n (

m /

12

0 d

ay

s)

Bright

Hot dip

zinc

Model

steel

model



CSE 97

Figure C.4.3 Comparison of corrosion model for embedded metal,with test data for CCA

treated Radiata pine.

CSE 98

Appendix D:. Model Equations 2002

D.1 Hazard Zones

To simplify the calculation procedure, 3 hazard zones, namely A, B and C; are created as

shown in Fig. D.1.1. This original map - similar to the SEMC map in Fig. C.3.3 - is plotted

from the SEMCmean data of the Bureau of Meteorology (BOM). However, there has been an

adjustment in the SEMCmean data due to the simplification of the climate zones. The

adjustment has been made to the tropical areas, which have latitudes less than 23˚ S. The

SEMCmean data in the tropical areas has been increased 1% to compensate for using the

simplified values of Δmicroclimate for climate zone „other‟, ie. non-marine, as in Table D.4.3.3.

This will be defined as the effective SEMC. The simplified climate zonation is presented in

the next section.

A B

C

Figure D.1.1. „Original‟ hazard zone map based on SEMCmean.

Furthermore, expert opinions (MacKenzie, private communication) suggested that zone C

should not be cut out along the coast near Brisbane. Figure D.1.2 is the modified map

currently used in the Compendium. The modification was made by adjusting the effective

SEMCmean at Gympie (BOM data point C62) from 12.38% to 13%. The boundary and the

zone effective SEMCmean values are in Table D.1.1.

CSE 99

Figure D.1.2. Modified Hazard zone map based on effective SEMCmean - currently used in

the Compendium.

Table D.1.1 Effective SEMCmean values for the 3 hazard zones

Zone Zone effective

SEMCmean

Effective SEMCmean

used for boundary

A

B

C

9

12

15

10

13

D.2 Climate Zones

The climate zonation procedure with 6 zones as presented in Table 1.3.5 is simplified by

defining only 2 climate zones:



D.3 Material Grouping

See Section 2.3.2 for timber classification based on acidity.

D.4 Simplified Theory Equations

CSE 100

This section provides the simplified version of the theoretical equations in Appendix C to be

used for the calculation in the 2002‟s Compendium (Leicester et.al. 2002).

D.4.1 The Base Model of Embedded corrosion in untreated wood

The corrosion depth of connectors embedded in untreated wood subjected to 120-day

corrosion, f120(M), is:

f120(M) = 0 if M < Mo (D.4.1.1)

f120(M) = C120 if M Mo (D.4.1.2)

where M is moisture content. The function is illustrated in Figure D.4.1.1. Table D.4.1.1 gives

parameters of the model calculated by Eqs.(1.3.3) to (1.3.10), using representative pH values

in Table D.3.2.


M

M0

C120


f120(M)

In untreated wood

Figure D.4.1.1. Base model of embedded corrosion in untreated wood.

Table D.4.1.1 Parameters of the corrosion model of embedded fasteners in untreated wood

Parameter pH Zinc connector Steel connector

Hardwood Softwood Hardwood Softwood

C120

Acidity class 1

Acidity class 2

Acidity class 3

5.5

4.5

3.5

1.7

8.6

12.5*

4.2

5.0

6.0

1.6

9.3

16*

1.7

5.5

13*

M0 (%) 10 15 15 20 (*) Values adjusted to the available measured data. The values calculated from Eqs. (1.3.3), (1.3.5) and (1.3.6) are

unacceptable high (43.5, 53.0, and 18.0, respectively), where the assigned pH of 3.5 for acidity class 3 species

appear to be out of valid range of the equations.

D.4.2 The Base Model of Embedded Corrosion in CCA treated wood

The model for of zinc connectors embedded in CCA treated wood is given by:

f120(M) = 0 if M < 10 (D.4.2.1)

f120(M) = 0.7 (M-10) if M 10 (D.4.2.2)

The model for of steel connectors embedded in CCA treated wood is given by:

f120(M) = 0 if M < 13 (D.4.2.3)

CSE 101

f120(M) = 0.7 (M-13) if M 13 (D.4.2.4)

where M is moisture content. The function is illustrated in Figure D.4.2.1.


M (%) 10

C120


f120(M)

In CCA treated wood

wood

13

Zinc Steel

0.7

Figure D.4.2.1. Base model of embedded corrosion in CCA-treated wood.

D.4.3 Moisture Content of Timber

The surface equilibrium moisture content (SEMC) for a given temperature and humidity is

calculated according to Bramhall‟s equation as follows:

ee 2

e

log ( /100) 0.0251log

17.884 0.0002362( 273) 0.1432( 273)

0.92 log 1.0327 0.000674( 273)

H

T TSEMC

T

(D.4.3.0)

where



The SEMC can be calculated with time, using data from a nearby Bureau of Meteorology

station, and then be averaged to obtain SEMCmean, the mean annual value of the surface

moisture contents. From Eq.(1.3.16), the maximum and the mean seasonal moisture contents

of a piece of timber for one year are:

TMmean = exp[A + B SEMCmean] (D.4.3.1)

TMmax = exp[A + B SEMCmax] (D.4.3.2)

SEMCmax = SEMCmean +2 (D.4.3.3)

Where TMmax = the maximum value out of the four TM seasonal values of moisture content in

a piece of timber for one year, TMmean = the mean annual value of timber moisture content.

The mean surface equilibrium moisture content, SEMCmean, can be computed from BOM data

using the procedure above with Eq.(D.4.3.0); or taken the representative value given in Table

D.4.3.1. The moisture content parameters A and B are provided in Table D.4.3.2.

The maximum and mean seasonal moisture contents of timber in building, BTMmax and

BTMmean, are:

CSE 102

mean mean microclimate climate rain BTM TM (D.4.3.4)

max mean max mean BTM BTM D TM TM (D.4.3.5)

where the damping factor (D), the adjustment factors for the climate (climate) and

microclimate (microclimate) are given in Tables D.4.3.3. Values in Table D.4.3.3 are based on

simplifying Tables 1.3.3 and 1.3.4, noting the adjustment for SEMCmean of 1% for all areas

above 23˚ S, i.e. roughly for all „tropical‟ areas as defined in Fig.1.3.4.

The adjustment factor for rain (rain) is given in Table D.4.3.4, and used only for outdoor

structures (facades), which is divided into 3 types: structures sheltered or partly sheltered

from rain (such as house cladding), vertical structures exposed to rain (such as fencing), and

horizontal structures exposed to rain (such as decking). Values of this factor are resulted from

the reality checks with expert opinions as presented in Section D.5. For other microclimates,

including sub-floor, wall cavity, and roof space, rain = 0.

For determining the above factors, it is necessary to know the Hazard zone and Climate zone

of the structure. The Hazard zonation and map are presented in Section D.1, and the Climate

zonation is presented in Section D.2

Table D.4.3.1 Mean surface equilibrium moisture content

Hazard zone SEMCmean

A

B

C

9

12

15

Table D.4.3.2 Moisture content parameters A and B

Moisture Content

Parameter Hardwoods Softwoods CCA Treated Pine

A 1.84 1.78 2.00

B 0.05 0.054 0.045

Table D.4.3.3 Damping factor and adjustment factor for climate and micro-climate

Microclimate D Δclimate Δmicroclimate

Marine(1)

Other Marine Other Marine Other

Sub-floor

Wall cavity

Roof space

Outdoor

2.0

1.5

2.0

6.0

1.0

1.5

2.0

2.0

2.0

2.0

2.0

2.0

0

0

0

0

0.5

-1.5

-2.5

0.5

1.5

1.0

-2.5

0.5 (1) If distance to coast < 1km, then climate zone is „Marine‟; otherwise, climate zone is „Other‟

Table D.4.3.4 Adjustment factor rain

Outdoor (Facades)

Microclimate

Adjustment factor rain





0

1

3

1

4

9

2

8

17

CSE 103

D.4.4 Corrosion Depth


c = co tn (D.4.4.1)

where n= 0.5 for zinc and n = 0.6 for steel; co is corrosion depth for the first year (mm)

computed as follows,


o 120 max 120 mean( ) 0.3 ( ) c f BTM f BTM (D.4.4.2)

For the case of treated wood:

o 120 mean2.5 ( )c f BTM (D.4.4.3)

where f120 is defined by Eqs. (D.4.1.1) and (D.4.1.2) for untreated wood case and

Eqs.(D.4.2.1) to (D.4.2.4) for CCA treated wood case.

D.5 Modification due to Expert Opinions

The following facts provided by expert opinions (MacKenzie, 2002) have been considered to

further extend and calibrate the score system for outdoor structures. They are:

„A HDG (Hot-Dip Galvanised) nail in a treated pine deck exposed to rain in Brisbane

would be expected to last about 15 years, on a fence we would expect 25 years. For

plain bright nail, probably 5 years less‟.

„For plain nails in Hardwoods fencing up here (Brisbane) I would expect about 30 years

and for HDG nails in exposed hardwood decking around 30 years‟.

„Plain nails punched, puttied and pained cladding on houses, hardwood or cypress

cladding/frame > 100 years‟

„For treated pine cladding on houses fixed with HDG nails, would expect 50+ years‟

The extension and calibration of the score system were carried out for outdoor microclimate.

The outdoor structures are divided into 3 groups: (1) Sheltered / partly sheltered to rain, (2)

Exposed to rain - Vertical surface (e.g. fencing) and (3) Exposed to rain - Horizontal surface

(e.g. decking). The target of the calibration was to match the computed service lives of the

fasteners to the above facts provided by the expert opinions.

The extension and calibration were resulted in the introduction of the adjustment factor for

rain, rain, to the theory equations, and its recommended values are listed in Table D.4.3.4.

CSE 104

Appendix E:. Hazard Score System 2002

E.1 Definition of Hazard Scores

Table E.1.1 gives the total hazard scores for various scenarios of the corrosion in embedded

fasteners. Derivation of this table is presented in Appendix A.

Table E.1.1 Hazard scores for corrosion of embedded fasteners as used in the 2002

Compendium (Leicester et.al. 2002)

Microclimate(1)

Total Hazard scores

Zone A(2)

Zone B(2)

Zone C(2)

Marine(3)

Other Marine Other Marine Other

Subfloor

Wall cavity

Roof space

14

12

11

12

12

9

16

14

13

14

14

11

18

16

15

16

16

13

Outdoors

Sheltered / partly sheltered (4)



19

20

22

12

13

15

22

25

30

15

18

23

25

31

40

18

24

33

(1) For information on the building envelope, see Section 5.1 in the 2002 Compendium

(2) See hazard zone map in Figure D.1.2

(3) Climate zone is „Marine‟ when distance to coast < 1km

(4) e.g. house cladding

(5) e.g. fencing

(6) e.g. decking

E.2 Definition of Hazard Class

For ease of application to service life prediction of various types of fastener, the selection of

hazard class limit have been decided to have the same limits for steel and zinc, but to have

different limits for types of wood. The definition of hazard classes and their boundaries in

terms of the total scores for embedded corrosion of fasteners have been chosen as shown in

Table E.2.1 and illustrated in Figures E.2.1 and E.2.2 for zinc and steel fasteners, respectively.

It is noted that to have the same hazard class limits for both zinc and steel fasteners embedded

in untreated wood, the hazard class H3 acts as a „buffer‟ class located near or right at the

„jumping steps‟ of the theoretical values of c0. This is somewhat a compromising solution for

practical uses, and justified because such sudden jumping steps of c0 would not be true in

reality.

CSE 105

Table E.2.1 Definition of hazard ratings

Hazard rating

Hazard score

In untreated timber CCA-treated

timber Eucalypts Other

hardwoods Softwoods

H1

H2

H3

H4

H5

na

<12

12~15

>15

na

na

<12

12~15

>15

na

na

<16

16~20

>20

na

<12

12~17

18~23

24~30

>30

Zinc in Eucalypts

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35 40

Total Score

c0

H2 H3 H4

Zinc in Non-Euc. Hardwoods

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35 40

Total Score

c0

H2 H3 H4

Zinc in Softwoods

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35

Total Score

c0

H2 H3 H4

Zinc in CCA-treated Woods

0

5

10

15

20

25

30

35

40

45

0 5 10 15 20 25 30 35 40

Total Score

c0

H1 H2 H3 H4 H5

Figure E.2.1. Hazard ratings for zinc fasteners embedded in different types of wood

CSE 106

Steel in Eucalypts

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35 40

Total Score

c0

H2 H3 H4

Steel in Non-Euc. Hardwoods

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35 40

Total Score

c0

H2 H3 H4

Steel in Softwoods

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35 40

Total Score

c0

H2 H3 H4

Steel in CCA-treated Woods

0

5

10

15

20

25

30

35

40

45

0 5 10 15 20 25 30 35 40

Total Score

c0

H1 H2 H3 H4 H5

Figure E.2.2. Hazard ratings for steel fasteners embedded in different types of wood

CSE 107

E.3 Derived c0 values for the 2002 Compendium (Leicester et.al. 2002)

Based on the theoretical values of c0 varying in each hazard class, representative values of c0

for the classes are assumed and presented in Tables E.3.1 and E.3.2 for zinc and steel,

respectively.

Table E.3.1 The first-year corrosion depth of embedded zinc fasteners– as used in the


Hazard rating


Untreated timber CCA-treated timber

Eucalypts Others

H1

H2

H3

H4

H5

na

0

12

16

na

na

0

4

6

na

0

8

20

30

40

Table E.3.2 The first-year corrosion depth of embedded steel fasteners – as used in the


Hazard rating


Untreated timber CCA-treated timber

Eucalypts Others

H1

H2

H3

H4

H5

na

0

15

20

na

na

0

7

10

na

0

5

15

25

35

E.5 Service life








Manual 6 – Embedded corrosion of fasteners in …€¦ · Manual 6 – Embedded corrosion of fasteners in exposed timber structures PROJECT NUMBER: PN07.1052 August 2007 MARKET

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